Obvious things C should do
digitalmars.com
digitalmars.com
Being able to just read through a library's .h files to know how to use it is really nice. Typically, my .h files don't really look like my .c files because all the documentation for how to use the thing lives in the .h file (and isn't duplicated in the .c file). It would be entirely possible to put this documentation into the .c file, but it makes reading the interface much less pleasant for someone using it.
I always found this argument baffling, because the way some other language solve this problem is with tooling, which is a much better way to do it in my opinion.
Take Rust for example. You want to see the interface of a given library and see how to use it? Easy. Type in `cargo doc --open` and you're done. You get a nice interface with fully searchable API interface with the whole public API, and it's all automatic, and you don't have to manually maintain it nor have to duplicate code between your header and your source file.
I used to be a big fan of doxygen etc, but for the stuff I've worked on, I've found that "pretty" documentation is way less important than "useful" documentation, and that the reformatting done by these tools tends to lead towards worse documentation with the people I have worked with ("Oh, I need to make sure every function argument has documentation, so I will just reword the name of the argument"). Since moving away from doxygen I have stopped seeing this behaviour from people - I haven't tried to get a really good explanation as to why, but the quality of documentation has definitely improved, and my (unproven) theory is that keeping the presentation as plain as possible means that the focus turns to the content.
I don't know if rust doc suffers the same issues, but the tooling you are mentioning just seems to add an extra step (depending on how you count steps I suppose, you could perhaps say it is the same number of steps...) and provide no obvious benefit to me (and it does provide the obvious downside that it is harder to edit documentation when you are reading it in the form you are suggesting).
But with all these things, different projects and teams and problem domains will probably tend towards having things that work better or worse.
The problem with this is no one agrees on the definition of "well-written", so consistency is a constant battle and struggle. Language tooling is a better answer for quality of life.
It is one of those things that sounds "obviously true", but in practice I've found that it doesn't really live up to the promise. As a concrete example of this, having a plain text header file as documentation tends to mean that when people are reading it, if they spot a mistake or see that something isn't documented that should be documented, they are much more likely to fix it than if the documentation is displayed in a "prettier" form like HTML.
The problem with header files that aren't "well-written" tends to be that the actual content you are looking for isn't in there, and no amount of language tooling can actually fix that (and can be an impediment towards fixing it).
GitHub readmes? Bring on the weird quirks, art, rants about other software, and so on. I’ll take it all.
Don’t get me started on linters. Yes, there’s lots of things that should actually be consistent in a codebase (like indentation). But for every useful check, linters have 100 random pointless things they complain about. Oh, you used a ternary statement? Boo hoo! Oh, my JavaScript has a mix of semicolons and non semicolons? Who cares? The birds are singing. Don’t bother me with this shite.
Software is a creative discipline. Bland software reflects a bland mind.
> Oh, my JavaScript has a mix of semicolons and non semicolons? Who cares?
i had to refactor and port a javascript codebase that contained a mix of all of javascripts syntactic sugar, no comments anywhere in the codebase, and i was unable to ask the original devs any questions. the high amount of syntactic sugar gave me "javascript diabetes" - it was fun figuring out all the randomness, but it delayed the project and has made it extremely difficult to onboard new folks to the team after i completed the port.
painting is a creative discipline, and the mona lisa has stood the test of time because davinci used a painting style and materials that set the painting up for long term use.
a codebase without standards is akin to drawing the mona lisa on a sidewalk with sidewalk chalk.
any advice on how to implement an auto linter in an old codebase? i hate losing the git blame info.
The historical way is to have a .ml and a .mli files. The .ml file contains the implementation. Any documentation in that file is considered implementation detail, will not be published by ocamldoc. The .mli file contains everything users need to know, including documentation, function signatures, etc.
Interestingly, the .mli and the .ml signatures do not necessarily need to agree. For instance, a global variable in the .ml does not need to be published in the .mli. More interestingly, a generic function in the .ml does not need to be exposed as generic in the .mli, or can have more restrictions.
You could easily emulate this in Rust, but it's not the standard.
That seems like an orthogonal issue to me. I've seen places where documentation is only in the source code, no generated web pages, but there is a policy or even just soft expectation to document every parameter, even if it doesn't dd anything. And I've also seen places that make heavy use of these tools that doesn't have any such expectation.
No, you can't, and it's not even close.
You have a header file that's 2000 lines of code, and you have a function which uses type X. You want to see the definition of type X. How do you quickly jump to its definition with your "any old text editor"? You try to grep for it in the header? What if that identifier is used 30 times in that file? Now you have to go through all of other 29 uses and hunt for the definition. What if it's from another header file? What if the type X is from another library altogether? Now you need to manually grep through a bunch of other header files and potentially other libraries, and due to C's include system you often can't even be sure where you need to grep on the filesystem.
Anyway, take a look at the docs for one of the most popular Rust crates:
https://docs.rs/regex/1.11.1/regex/struct.Regex.html
The experience going through these docs (once you get used to it) is night and day compared to just reading header files. Everything is cross linked so you can easily cross-reference types. You can easily hide the docs if you just want to see the prototypes (click on the "Summary" button). You can easily see the implementation of a given function (click on "source" next to the prototype). You can search through the whole public API. If you click on a type from another library it will automatically show you docs for that library. You have usage examples (*which are automatically unit tested so they're guaranteed to be correct*!). You can find non-obvious relationships between types that you wouldn't get just by reading the source code where the thing is defined (e.g. all implementations of a given trait are listed, which are usually scattered across the codebase).
> I don't know if rust doc suffers the same issues, but the tooling you are mentioning just seems to add an extra step (depending on how you count steps I suppose, you could perhaps say it is the same number of steps...) and provide no obvious benefit to me (and it does provide the obvious downside that it is harder to edit documentation when you are reading it in the form you are suggesting).
Why would I want to edit the documentation of an external library I'm consuming when I'm reading it? And even if I do then the effort to make a PR changing those docs pales in comparison to the effort it takes to open the original source code with the docs and edit it.
Or did you mean editing the docs for my code? In that case I can also easily do it, because docs are part of my source files and are maintained alongside the implementation. If I change the implementation I have docs right there in the same file and I can easily edit them. Having to open the header file and hunt for the declaration to edit the docs "just seems to add an extra step" and "and provide no obvious benefit to me", if I may use your words. (:
I am not making things up when I say that the very first question I had about how to use this module, either is not answered, or I couldn't find the answer. That question was "what regular expression syntax is supported?". This is such a fundamental question, yet there is no answer provided.
As a preference thing, I don't really like examples in APIs (it is supposed to be a reference in my opinion) and I find them to be mostly noise.
> Why would I want to edit the documentation of an external library I'm consuming when I'm reading it? And even if I do then the effort to make a PR changing those docs pales in comparison to the effort it takes to open the original source code with the docs and edit it.
Right, this is possibly where our experiences differ. I'm frequently pulling in loads of code, some of which I've written, some of which other people have written, and when I pull in code to a project I take ownership of it. Doesn't matter who wrote it - if it is in my project, then I'm going to make sure it is up to the standards I expect. A lot of the time, the code is stuff I've written anyway, which means that when I come back in a few months time and go to use it, I find that things that seemed obvious at the time might not be so obvious, and a simple comment can completely fix it. Sometimes it is a comment and a code change ("wouldn't it be nice if this function handled edge case X nicely? I'll just go in there and fix it").
The distinction between external and internal that you have looks pretty different to me, and that could just be why we have different opinions.
This is a fair question to have. As others have already said, this is the API reference for a particular class, so you won't get the high level details here. You can click in the upper left corner to go to the high level docs for the whole library.
> The distinction between external and internal that you have looks pretty different to me, and that could just be why we have different opinions.
Well, there are two "external" vs "internal" distinctions I make:
1. Code I maintain, vs code that I pull in as an external dependency from somewhere else (to give an example, something like libpng, zlib, etc.). So if I want to fix something in the external dependency I make a pull request to the original project. Here I need to clone the original project, find the appropriate files to edit, edit them, make sure it compiles, make sure the tests pass, make a PR, etc. Having the header file immediately editable doesn't net me anything here because I'm not going to edit the original header files to make the change (which are either installed globally on my system, or maintained by my package manager somewhere deep under my /home/).
2. Code that is part of my current project, vs code that is a library that I reuse from another of my projects. These are both "internal" in a sense that I maintain them, but to my current project those are "external" libraries (I maintain them separately and reuse in multiple projects, but I don't copy-paste them and instead maintain only one copy). In this case it's a fair point that if you're browsing the API reference it's extra work to have to open up the original sources and make the change there, but I disagree that it's making things any harder. I still have to properly run any relevant unit tests of the library I'm modifying, still have to make a proper commit, etc., and going from the API reference to the source code takes at most a few seconds (since the API reference will tell me which exact file it is, so I just have to tell my IDE's fuzzy file opener to open up that file to me.) and is still a tiny fraction of all of the things I'd need to do to make the change.
The main page for the documentation answers that question: https://docs.rs/regex/1.11.1/regex/index.html
It even says "If you just want API documentation, then skip to the Regex type", which is what you were linked to before.
Personally I'm quite content with both experiences. But it really is just a matter of preference.
But also, they probably to know how to keep their dependencies sane, and possibly think the best way to document that giant 2k lines interface is in a book. What are both really good opinions, that will never be really "understood" by communities the GP takes his libraries from just because it's not viable for them to do it.
^struct whateverwould you make the same argument for java then?
(You could imagine such a representation, i.e. remove all method bodies and (package-)private elements, but the result wouldn’t be valid Java. IDEs arguably could and should provide such a source-level view, e.g. via code folding, but I don’t know any that do.)
Java also has too many tools for this. You both have class/interface, but also public/private. I honestly think C does it better than Java.
really? I know java pretty well, and there aint nothing weird there.
C uses conventions to produce an "interface" (ala a header file with declarations). Java uses compilers to produce an interface, which i do really like. You can ship that interface without an implementation, and only at runtime load an implementation for example.
> You both have class/interface, but also public/private.
And these are all othorgonal concerns. A private interface is for the internal organization of code, as opposed to a public one (for external consumption). That's why you might have a private interface.
You can do this in C as well, since it has separate code declarations and definitions. You conventionally put the declarations in the header and definitions in the source file. A C program can link against declarations alone, and the implementations can be loaded later using dynamic linking.
> And these are all othorgonal concerns. A private interface is for the internal organization of code, as opposed to a public one (for external consumption). That's why you might have a private interface.
But these are profoundly overlapping concerns. Interfaces also hide the internal organization of the code, and on top of this, you also have project jigzaw's modules (that absolutely nobody uses), but which also caters toward separating private implementations from public interfaces.
of course javadoc can answer the same questions but then you have to run it.
By now, of course, precompiled headers exist, but their interplay with #define allows for fun inconsistencies.
And, of course, they leak implementation as much as the author wants, all the way to .h-only single-file libraries.
If you want an example of a sane approach to separate interface and implementation files from last century, take a look e.g. at Modula-2 with its .int and .mod files.
They encourage the use of large header files that group unrelated concerns. In turn that makes small changes in header files produce massive, unnecessary rebuilds of zillions of object files.
The clean practice is to push down #includes into .c files, and to ruthlessly eliminate them if at all possible. That speeds up partial rebuilds enormously. And once you adopt that clean practice, pre-compiled headers yield no benefit anyway.
Human readable headers are accessible out of context if the implementation. They also help provide a clear abstraction - this is the contract. This is what I support as of this version. (And hopefully with appropriate annotations across versions)
The "what if you don't have the tool" situation never happens in case of Rust. If you have the compiler you have the tool, because it's always included with the compiler. This isn't some third party tool that you install manually; it's arguably part of the language.
> What if there’s a syntax error in some implementation or dependency such that the tool chokes early?
In C I can see how this can happen with its mess of a build systems; in Rust this doesn't happen (in my 10+ years of Rust I've never seen it), because people don't publish libraries with syntax errors (duh!).
In this specific case, your tool requires a web browser (though I'm assuming that there is a non-web browser form of what is being sold here). Maybe you are in a situation where you only have terminal access to the machine.
Maybe you are on your phone just browsing github looking for a library to use
I'm sure people can continue to imagine more examples. It is entirely possible that we have different experiences of projects and teams.
Hopefully they’ll imagine more compelling examples.
If the hypothetical person’s phone is capable of browsing GitHub, I don’t see why they can’t also browse docs.rs. It renders well on small screens. That’s not a hypothetical, I’ve actually read the docs for libraries on my phone.
So it’s built into GitLab and GitHub? BitBucket? How easy is it to use on windows (i.e. is it is easy as opening a .h in notepad and reading it)? How easy is it to use from a command line environment with vim or emacs bindings?
I could go on. “Never” is doing a lot of heavy lifting in your assertion. I shouldn’t have to install a toolchain (let alone rely on a web browser) to read API documentation.
Please do. It just sounds like you’re nitpicking.
If you can open a browser, open docs.rs. The GitHub repo usually contains a link to docs.rs because that’s how people prefer to read the documentation.
If you prefer working without the internet that’s fine too. Use cargo doc, which opens the rendered doc page in a local web browser.
If you prefer being in a text editor exclusively, no problem! Grep for `pub` and read the doc comments right above (these start with ///). No toolchain necessary.
Look, most normal people don’t have some intense phobia of web browsers, so they’d prefer docs.rs. For the people who prefer text editor, it’s still a great experience - git clone and look for the doc comments.
The point is, the existence of docs.rs only encourages Rust library developers to write more and better documentation, which everyone, including text editor exclusive people benefit from. That’s why your comment sounds so strange.
No. It's built into the toolchain which every Rust developer has installed.
> How easy is it to use on windows (i.e. is it is easy as opening a .h in notepad and reading it)?
A easy as on Linux or macOS from my experience.
> How easy is it to use from a command line environment with vim or emacs bindings?
Not sure I understand the question; use how exactly? You either have a binding which runs `cargo doc` and opens the docs for you, or you use an LSP server and a plugin for your editor in which case the docs are integrated into your editor.
> I shouldn’t have to install a toolchain (let alone rely on a web browser) to read API documentation.
If you want you can just read the source code, just as you do for any other language, because the docs are right there in the sources.
For publicly available libraries you can also type in `https://docs.rs/$name_of_library` in your web browser to open the docs. Any library available through crates.io (so 99.9% of what people use) have docs available there, so even if you don't have the toolchain installed/are on your phone you can still browse through the docs.
I know what you're going to say - what if you don't have the toolchain installed and the library is not public? Or, worse, you're using a 30 year old machine that doesn't have a web browser available?! Well, sure, tough luck, then you need to do it the old school way and browse the sources.
You can always find a corner case of "what if...?", but I find that totally unconvincing. Making the 99.9% case harder (when you have a web browser and a toolchain installed, etc.) to make the 0.1% case (when you don't) easier is a bad tradeoff.
"you always have the exe" is just not even remotely a valid argument.
Why? Can you explain it to me?
I'm a Rust developer. I use my work station every day for 8 hours to write code. I also use `cargo doc` (the tool for which "I always have the exe") every day to look up API docs, and in total this saves me a ton of time every month (probably multiple hours at least, if I'm working with unfamiliar libraries), and I save even more time because I don't have to maintain separate header files (because Rust doesn't have them).
Can you explain the superior flexibility and utility of "merely opening a text file" over this approach, and how that would make me (and my colleagues at work) more productive and save me time?
I'm not being sarcastic here; genuinely, please convince me that I'm wrong. I've been a C developer for over 20 years and I did it the "opening a text file" way and never want to go back, but maybe you're seeing something here that I never saw myself, in which case please enlighten me.
It's not less flexible once you already took availability into account.
It has more utility, that's the entire point.
There are a few people in this thread, including you, who claim that they vastly prefer the output of documentation to be plain text in a single file rather than linked HTML files OR reading the source in multiple plaintext files.
That’s a preference, so y’all can’t be wrong. But consider that if this preference was even slightly popular, cargo doc would probably get a —-text option that output everything in a single text file. The fact that it doesn’t have it tells me that this preference is very niche.
It works with every syntax that you can compile, because it uses the compiler itself to extract the documentation.
Yes, it works on Windows too. Rust supports Windows as a first-class platform. It works with dependencies too (the docs even link across packages). The fragmentation of C tooling and unreliability/complexity of integrating with C builds is not a universal problem.
Rust's built-in documentation generator creates HTML, so anything with a browser can show it. It also has JSON format for 3rd party tooling.
The same language syntax for the documentation is understood by Rust's LSP server, so vim, emacs, and other editors with LSP plugins can show the documentation inline too.
I've been using this for years, and it works great. I don't miss maintaining C headers at all. I write function definitions once, document them in the same place where the code is, and get high fidelity always up-to-date API docs automatically.
Why are you reading a library API for a language you're not coding in?
I'm sure you can come up with some situation, but that situation should NOT be what we optimize for.
And web browsers are fine.
> is it is easy as opening a .h in notepad and reading it
If you include the actual ease of reading, yeah it should be.
Most programming language communities are okay with expecting a certain amount of (modern) tooling, and C can't rely on legacy to remain relevant forever...
However the tooling experience is pretty much ~1995, with the difference IDL is at version 3.0.
Frankly your description of what you just called easy sounds terrible and pointlessly extra, indirection that doesn't pay for itself in the form of some overwhelming huge win somewhere else. It's easy only if the alternative was getting it by fax or something.
I do enjoy using C but that is one area where it should have been better designed.
The way C handles header files is sort of "seems-to-work" by just blindly including the text inline.
I know this is not a much-used language, but in comparison, Ada did a pretty nice thing. They have the concept of packages and package bodies. The package is equivalent to the header file, and the package body is the implementation of the package.
I remember (long ago when I used ada) that everyone could compile against the package without having the package body implementation ready so the interfaces could all work before the implementation was ready.
an in another direction, I like how python does "header files" with "import". It maps easily to the filesystem without having to deal with files and the C include file semantics.
In my experience, having a header file nudges you to think about interface being a _different thing_ to implementation - something that (because you need to) you think about as more fundamentally separate from the implementation.
Folks who think this way bristle at the idea that interface be generated using tooling. The interface is not an artifact of the implementation - it’s a separate, deliberate, and for some even more important thing. It makes no sense to them that it be generated from the implementation source - that’s an obvious inversion of priority.
Of course, the reverse is also true - for folks used to auto-generated docs, they bristle at the idea that the interface is not generated from the one true source of truth - the implementation source. To them it’s just a reflection of the implementation and it makes no sense to do ‘duplicate’ work to maintain it.
Working in languages with or without separate interface files nudges people into either camp over time, and they forget what it’s like to think in the other way.
I think it is telling that the handful of languages that still have something akin to .h files use them purely to define cross-language APIs.
Or it can be generated either as text, or graphical tooling, Object Pascal, D, Haskell, Java, C#, F#, Swift, Go, Rust.
All with stronger typing, faster compilation (Rust and Swift toolchain still need some work), proper namespacing.
Unfortunately C tooling has always been more primitive than what was happening outside Bell Labs, and had AT&T been allowed to take commercial advantage, history would be much different, instead we got free lemons, instead of nice juicy oranges.
At least they did come up with TypeScript for C, and it nowadays supports proper modules, alongside bounds checked collection types.
When maintaining the code that means I have to go to a separate file to read what a function is supposed to do, or update the documentation.
And when reading the documentation, if the documentation is unclear, I have to go to a separate file to see what the function actually does.
Granted, the implementation can get in the way if you are just reading the documentation, but if you aren't concerned about the implementation, then as others have said, you can use generated documentation.
Maintaining header files is tedious and I often resorted to a kind of “OBHF.h” for common types, if you know what I mean. Otherwise it’s too much cross-tangling and forwards. Even in ts I do type-only src/types.ts for types likely common to everything, mostly because I don’t want pages of picky this-from-there this-from-there imports in every module.
As for public/private and sharing “friends” across implementation modules, we didn’t invent anything good anyway. I just name my public private symbols impl_foo and that tells me and everyone what it is.
That said, I wouldn’t want to make html out of it like these *-doc tools do. Using another program to navigate what is basically code feels like their editor sucks. My position on in-code documentation is that it should be navigatable the same way you write it. External tools and build steps kill “immersion”.
Basically, I cannot do something like a struct with an opaque internal structure but a compile time known layout so that the compiler can optimise it properly but the user cannot mess with the internals (in language supported direct ways).
If you want to have some abstract type where you don't let people know anything about the innards, but you do have an explicit interface which enumerates what you can do with it, then yes - you can only really pass around pointers to these things and people outside your abstraction can only pass references not values.
If you want people to be able to pass your abstract type by value (among other things), then either you need to let them know how big the thing is (an implementation detail) or you have to expose the copy implementation in such a way that it could be inlined (more implementation details).
Sometimes, the "pure abstraction" approach is best where you only ever deal with pointers to things, and other times the "let's pretend that people do the right thing" approach is best. I don't see this as a header file thing though.
In a header file, the information for the compiler and the user are the exact same which means you can't reduce your public interface without straight up hiding more of yourself.
Let the header files be written for people to read first, and only if there is actually a big performance issue, and the problem is the interface do you need to revisit it (and I'm not just saying this - I will frequently and happily go back and modify interfaces to allow for less data movement etc, but most of the time it really isn't important).
I think you are probably right to disagree with me though - I think I should have said that it is more of a limitation on how object files work, rather than how machines work. Object files aren't the only way things can work.
With C++ you have the third option where the compiler makes sure that the "people will do the right thing" with the private keyword - assuming they're not doing some weird pointer math to access the private members..
Of course, you'll have to deal with ABI stability now but it's all tradeoffs for what your requirements are.
It comes down to a cost benefit thing - is the cost of poorer readability worth it for mitigating the risk of people doing the wrong thing? My experience says no, other people's experience says yes. Probably we are working on different problems and with different teams.
The problem is real for C++.
Optimizers can look across translation units nowadays (link-time optimization), so there is no reason to expose internal details in a header for this. For dynamic libraries this does not work of course, but it also shouldn't.
And then there are cases where (often die to performance) you want inlining of some operations without relying on Link time optimisation, then implementation has to go to headers, too.
Of course you can also have internal header-files within your own project, which you don't share with the end-users of your product.
Modula-2 modules are based on Xerox Mesa, and do have split sections, as does Ada.
Additionally, Modula-2 and Ada modules/packages have a powerful feature that is seldom used, multiple interfaces for the same module implementation, this allows to customise the consume of a module depending on the customer code.
Yes, I remember the .tpu and .dcu filename extensions.
IIRC, .tpu stood for turbo pascal unit, and .dcu may have meant delphi compiled unit, not sure of the latter.
I don't remember the .int extension, but it would have been there, of course, if you say so.
What was the use of the .int file?
This page mentions a few ints without any context: https://comp.lang.pascal.borland.narkive.com/1B3WeJkX/rebuil...
This guy seems to package ints for documentation purposes: https://www.wrotniak.net/hplx/lxtpgr.html
Man this is nostalgic... T-T
You don't need header files for that.
A dead simple to write tool that parses the actual non-duplicating info, files, and prints you the interfaces and access qualifiers for each method as such, presenting you everything or just the public ones etc, should suffice.
Although it can infer types and generate the declaration fully
Evaluating Constant Expressions
- This seems really complicated...if you're working within a translation unit, thats much simplified, but then you're much more limited in what you can do without repeating a lot of code. I wonder how the author solves this.
Compile Time Unit Tests
- This is already somewhat possible if you can express your test as a macro, which if you add in the first point, then this becomes trivial.
Forward Referencing of Declarations
- I think there may be a lot of backlash to this one. The main argument against this is that it then changes the compiler from a one-pass to two pass compiler which has its own performance implications. Given the number of people who are trying to compile massive codebases and go as far as parallelizing compilation of translation units, this may be a tough pill for them to swallow. (evaluating constant expressions probably comes with a similar/worse performance hit caveat depending on how its done)
Importing Declarations
- This is a breaking change...one of the ways I have kind of implemented templating in C is by defining a variable and importing a c file, changing the variable, and then reimporting the same c file. Another thing I've done is define a bunch of things and then import the SQLite C Amalgamation and then add another function (I do this to expose a SQLite internal which isnt exposed via its headers). All of these use cases would break with this change.
Are there any thoughts about these issues? Any ways to solve them perhaps?
You are correct in that the source code to the function being evaluated must be available to the compiler. This can be done with #include. I do it in D with importing the modules with the needed code.
> This is already somewhat possible if you can express your test as a macro, which if you add in the first point, then this becomes trivial.
Expressing the test as a macro doesn't work when you want to test the function. The example I gave was trivial to make it easy to understand. Actual use can be far more complex.
> Performance
D is faster at compiling than C compilers, mainly because:
1. the C preprocessor is a hopeless pig with its required multiple passes. I know, I implemented it from scratch multiple times. The C preprocessor was an excellent design choice when it was invented. Today it is a fossil. I'm still in awe of why C++ has never gotten around to deprecating it.
2. D uses import rather than #include. This is just way, way faster, as the .h files don't need to be compiled over and over and over and over and over ...
D's strategy is to separate the parse from the semantic analysis. I suppose it is a hair slower, but it also doesn't have to recompile the duplicate declarations and fold them into one.
Compile time function execution can be a bottleneck, sure, but that (of course) depends on how heavily it is used. I tend to use it with a light touch and the performance is fine. If you implement a compiler using it (as people have done!) it can be slow.
> one of the ways I have kind of implemented templating in C is by defining a variable and importing a c file, changing the variable, and then reimporting the same c file. Another thing I've done is define a bunch of things and then import the SQLite C Amalgamation and then add another function (I do this to expose a SQLite internal which isnt exposed via its headers). All of these use cases would break with this change.
I am not suggesting removing #include for C. The import thing would be additive.
> Are there any thoughts about these issues?
If you're using hacks to do templating in C, you've outgrown the language and need a more powerful one. D has top shelf metaprogramming - and as usual, other template languages are following in D's path.
> You are correct in that the source code to the function being evaluated must be available to the compiler. This can be done with #include. I do it in D with importing the modules with the needed code.
> D's strategy is to separate the parse from the semantic analysis. I suppose it is a hair slower, but it also doesn't have to recompile the duplicate declarations and fold them into one.
I dont quite follow all the implications that these statements have. Does the compiler have a different way of handling a translation unit?
- Is a translation unit the same as in C, but since you're #including the file you would expect multiple compilations of a re-included C file? woudnt this bloat the resulting executable (/ bundle in case of a library)
- Are multiple translation units compiled at a time? Wouldnt this mean that the entire translation dependency graph would need to be simultaneously recompiled? Wouldnt this inhibit parallelization? How would it handle recompilation? What happens if a dependency is already compiled? Would it recompile it?
> Performance
I think a lot of this is tied to my question about compilation/translation units above, but from my past experience we have "header hygene" which forces us to use headers in a specific way, which if we do, we actually get really good preprocessor performance (a simple example being: dont use #include in a header), how would you compare performance in these kinds of situations vs a compiler without (i.e. either recompiled a full source file or looking up definitions from a compiled source)?
> If you're using hacks to do templating in C, you've outgrown the language and need a more powerful one. D has top shelf metaprogramming - and as usual, other template languages are following in D's path.
yes, as also demonstrated in the performance question, we do a lot to work within the confines of what we have when other tools would handle a lot more of the lifting for us and this is a fair criticism, but on the flip side, I dont have the power to make large decisions on an existing codebase like "lets switch languages" (even if for a source file or two...I've tried) as much as I wish I could, so I have to work with what I have.
We struggled with that for a long time with D. And finally found a solution. D can compile Standard C source files and make all the C declarations available to the D code. When I proposed it, there was a lot of skepticism that this could ever work. But when it was implemented and debugged, it's been a huge win for D.
> Performance
With D you can put all your source files on one command line invocation. That means that imports are only read once, no matter how many times it is imported. This works so well D users have generally abandoned the C approach of compiling each file individually and then linking them together. A vast amount of time is lost in C/C++ compilation with simply reading the .h files thousands of times.
Modules/imports are a gigantic productivity booster. They're not hard to implement, either. Except for the way C++ did it.
> re multiple translation units compiled at a time? Wouldnt this mean that the entire translation dependency graph would need to be simultaneously recompiled? Wouldnt this inhibit parallelization? How would it handle recompilation? What happens if a dependency is already compiled? Would it recompile it?
Yes, yes, yes, yes. And yet, it still compiles faster! See what I wrote above about not needing to read the .h files thousands of times. Oh, and building one large object file is faster than building a hundred and having to link them together.
I suppose in D this was less of an issue because D has pointers?
(The issue with return-by-pointer is that in C it's common to use the return value for an error code and use pointer arguments to pass data back to the caller. These are awkward to map to a target language that doesn't have pointers)
I think the idea is that compiling a translation unit produces two outputs, the object code (as it currently does), and an intermediate representation of the exported declarations, that could be basically a generated .h file, but it would probably be more efficient to use a different format. Then dependent translation units use those declaration files.
With this, you can still compile in parallel. You are constrained by the order of dependencies, but that is already kind of the case.
One complication is that ideally, if the signature doesn't change, but the implementation does, you don't need to re-compile dependent translation units. This is trivial if your build system detects changes based on content (like, say, bazel), but if it uses timestamps (like make) then the compiler needs to ensure the timestamp isn't updated when the declarations don't change.
But this really isn't a new concept. Basically every modern compiled language works fine without needing separate header files.
This is where the traditional distinction of "compiler vs Make" makes things harder; you want dependencies tracked at the "declaration" level, rather than the file level. If the timestamp _and_ content of the exported declarations file change, but none of the _used_ declarations changed, then there's no more compilation to be done. At best with file level tracking your build system will invoke the compiler for every downstream dependency, and they can decide if there's any more work to be done.
The build system would need to know which declarations are used (and what a declaration is) to do better.
As it turned out, though, people just found it too convenient to just import the .d file.
But as a very unexpected dividend, it was discovered that the D compiler would generate .di files from compiling .c files, and realized that D had an inherent ability to translate C code to D code!!!! This has become rather popular.
But in the context of that, what baffles me is the additions to the C Standard, such as useless (but complicated!) things like normalized Unicode identifiers, things with very marginal utility like generic functions, etc. Why those and not forward declarations?
I never want to do that again!
They are brittle and a maintenance nightmare. They did speed up compilations, though, but did not provide any semantic advantage.
With D I focused on fast compilation so much that precompiled headers didn't offer enough speedup to make them worth the agony.
I happened to be reading DMC source this week, those hydrate/dehydrate stuff really is everywhere (which I assume is solely used for precompiled headers?)
Yup. My compiler kept a list of which switches would perturb compilation and so would invalidate the precompiled header, and which did not.
Precompiled headers are an awful, desperate feature. Good riddance.
> topological order
You are correct. But its the reverse topological order, which is not the most readable ordering. One doesn't read a newspaper article starting at the bottom.
If I am writing some kind of service, I would write the main public functions first, using undefined functions in their bodies as needed. Then I would implement those functions below.
You don't often see
Answer = A + B,
where
A = ...
...
B = ...
For most other things, I usually prefer the bird-view first, when I am doing or reading some elses math.
Funnily the language Haskell which operates on definitions, is very order independent, it even allows circular definitions. I like it for leetcode and such.
Are modern C compilers actually still single pass?
All except ImportC, which effortlessly handles forward references. (Mainly because ImportC hijacks the D front end to do the semantics.)
The examples are quite simple in the article but I believe more complex cases would significantly degrade the compiler speed (and probably the memory footprint as well) and would require a VM to leverage this.
Which is probably assumed "too complex" to go into the standard. I'm not saying it's impossible, but I kind of understand why this would not go into any kind of standard.
> Importing Declarations
I wish C++ (or even C) would have gone into this direction instead the weird mess of what is defined for C++20.
Additionally you might import module into some symbol, like:
#import "string.c" as str
str.trim(" Hello World ");
This is totally tangential but I don't like when file paths are not explicit. In this specific case I don't know if I'm importing dex.d or dex.c.
Other popular languages can do it. That aside, it is an immensely popular and useful feature in D.
And yes, as one would expect, the more it is used, there's compile time speed and memory consumption required. As for a VM, the constant folder is already a VM. This just extends it to be able to handle function calls. C has simple semantics, so it's not that bad.
> Additionally
Great minds think alike! Your suggestions are just what D imports do. https://dlang.org/spec/module.html#import-declaration
> In this specific case I don't know if I'm importing dex.d or dex.c
This issue does come up. The answer is setting up your import path. It's analogous to the C compiler include path.
I'm pretty sure most production grade c compilers already do some level of compiler time evaluation for optimization. And C already has constant expressions.
I think a bigger hurdle would be that the compiler needs access to the source code of the function, so it would probably be restricted to functions in the same translation unit.
And then there is the possibly even bigger people problem of getting a committee with representives from multiple compilers to agree on the semantics of such constant evaluation.
> Which is probably assumed "too complex" to go into the standard. I'm not saying it's impossible, but I kind of understand why this would not go into any kind of standard.
I mean, it's basically 1:1 with the constexpr feature in C++. Almost every C compiler is already a C++ compiler, supporting constexpr functions and evaluation in C can't be that bad, can it?
void
test_load_uint8() {
npy_arr *arr = npy_load("tests/npy/uint8.npy");
assert(arr->n_dims == 1);
assert(arr->dims[0] == 100);
assert(arr->type == 'u');
npy_free(arr);
}
int
main(int argc, char *argv[]) {
PRINT_RUN(test_load_uint8);
...
}
struct S22079
{
int a, b, c;
};
_Static_assert(sizeof(struct S22079){1,2,3} == sizeof(int)*3, "ok");
_Static_assert(sizeof(struct S22079){1,2,3}.a == sizeof(int), "ok");
Could you have a look at fixing that?
I previously went down the rabbit hole of fancy unit test frameworks, and after a while I realised that they didn't really win much and settled on something almost identical to what you have (my PRINT_RUN macro has a different name, and requires the () to be passed in - and I only ever write it if the time to run all the tests is more than a second or so, just to make it really convenient to point the finger of blame).
The thing that I do which are potentially looked upon poorly by other people are:
1) I will happily #include a .c file that is being unit tested so I can call static functions in it (I will only #include a single .c file)
2) I do a tiny preprocessor dance before I #include <assert.h> to make sure NDEBUG is not defined (in case someone builds in a "release mode" which disables asserts)
If you can't write a test for functionality without fiddling with internal details the api is probably flawed
This logic is flawed. If you have an isolated implementation for some procedure that your api invokes in multiple places (or simply abstracted it out for clarity and SoC), it’s perfectly reasonable to test it separately even if it isn’t officially public.
I have something very similar.
https://github.com/ensisoft/detonator/blob/master/base/test_...
Borrowed heavily from boost.test.minimal and used to be a single header but but over the years I've had to add a single translation unit!
My takeaway is that if you keep your code base in a condition where tests are always passing you need much less complications in your testing tools and their error reporting and fault tolerance etc. !
These kinds of build-failing tests are great for your "I think I'm finished now" build, but not for your "I'm in the middle of something" builds (which are what 99% of your builds are).
It's like saying "You can't use the table saw until you put the drill away!"
i tend to disagree.
If you tried to express some thought but the compile time tests tells you you're wrong, you might actually just have an incomplete thought, or have not thought through all of the consequences of said expression.
It's basically what type-checking is in haskell - you cannot compile a program that does not type-check correctly. This forces you as a programmer, to always, and only, express complete thoughts. Incomplete, or contradictory thoughts cannot be expressed.
This should, in theory, lead to programs that are more well thought out. It also makes the program harder to write, because it forces the programmer to discover corners of their program for which they "know" isn't valid but don't care.
And this is precisely why I disagree with forcing it upon the developer at every stage of development. Generally, while in the thick of things, I just want to get things working with one part, not worry about what other parts this breaks (yet). But the pedantic "you have to fix this first" enforcement breaks my concentration because now I have to split my attention to things I don't want to even be bothered with yet. I'll get to it, but I sure as hell don't want you telling me WHEN I should.
One of the reasons could that you realize you don't need those parts, so it would have been a waste of time to write tests for them.
Is that the same as saying I don't want to have to write types either? Maybe. Types are like lightweight incomplete specs.
Or perhaps the parts existed, were useful, did have tests, and now a new feature requires refactoring that temporarily breaks things before I finally bring the house in order again. But I don't want to throw out the tests because parts of them may still be useful.
My point is, if the code is capable of being compiled and run, who is anyone to dictate that I shouldn't be allowed to run it (even broken) during my development cycle, just for some bureaucratic "I know better than you" reason?
This is the problem I see all over - people peer out from their limited perspective, assume that they see enough, and then make excessively restrictive policy decisions about what we can and cannot do. It's hubristic and so very, very annoying to the rest of us, especially since they also have a tendency to double-down, and there seems to be no way of getting through to them.
Why did you get out of your way to write tests about something that you don't want to be bothered about?
To me that is backwards. I prefer code written in a topological order for a number of reasons:
- It mirrors how you write code within a function.
- It's obvious where you should put that function in the module.
- Most importantly, it makes circular dependencies between pieces of code in a module really obvious.
I'm generally not a fan of circular dependencies, because they make codebases much more entangled and prevent you from being able to understand a module as a contained unit. In Python they can even lead to problems you won't see until you run the code[0], but circular imports are probably so common that current type checkers disable that diagnostic by default[1].
I think languages that don't support forward references (C, but also OCaml and SML) let me apply the "principle of least surprise" to circular dependencies. OCaml even disallows recursive dependencies between functions unless you declare the functions with "let rec fn1 = .. and fn2 = ..", which may be a bit annoying while you're writing the code but it's important information when you're reading it.
[0]: https://gist.github.com/Mark24Code/2073470277437f2241033c200...
[1]: https://microsoft.github.io/pyright/#/configuration?id=type-... (see reportImportCycles)
Defining functions on a “bottom-up” order like this is common even in languages like Python which allow forward references. [0]
Is that just a holdover from languages which don’t allow such references? Or does it actually make more sense for certain types of code?
Yes, so within a function you can refer to things that are defined later in the module. Isn't that's a "forward reference", even if the details are slightly different from how they work in D?
- add support for a slice type that encodes a pointer and length
- make re-entrant and ideally threadsafe APIs for things that currently use global state (including environment variables).
- standardize something like defer in go and zig, or gcc's cleanup attribute
- Maybe some portable support for unicode and utf-8.
The first could almost be done with macros. Except that separate declarations of an equivalent struct are considered different, so the best you cand do is a macro you can use define your owne typedef for a specific slice type. It could be done in the library if c supported something like a struct that had structural instead of nominal typing.
That one is easily broken. Pick a function that runs for a lloooonngg time...
int busybeaver(int n) {...} // pure function returns max lifetime of n state busy beaver machine
int x = busybeaver(99);Because D has a sizable runtime library and GC, which can be opted out of, but with very significant limitations, AFAICT.
I have a much better list for things to add to C: Nothing. C isn't perfect, or nearly as good as it could be, but simply adding things onto C gets you C++.
Adjusting what sircmpwn says: in C you don't solve problems by adding features, but by writing more code in C.
I liked an answer on stack overflow on a question on "how to write a generic function wrapper in Go", or something similar. Many suggestions included reflection, but the author wanted something simpler with varargs without reflection. A comment simply said: "wrong language".
I'd rather adopt this position for some languages, instead of add more and more to C3X. I do away with things in C23, and don't want even more things added in to C.
Making a strech of OP's arguments: "look at all this cool things that C could do, and that D does!". Well, go on and use D, nothing wrong with that.
(BTW, I do write test targets for every file in my C projects, but I'm not so much into jogging).
Those things aren't that obvious, and I'd rather not have them added to C.
Wrong language.
True, I know all about that. My Zortech C and C++ compiler was one pass (after the multiple preprocessing passes). The ground up ImportC C compiler completed a couple years ago has a separate parse pass.
So I well know the tradeoffs. The parser being stand-alone means it is much simpler to understand and unittest. I found no advantage to a single pass compiler. It isn't any faster.
> simply adding things onto C gets you C++
C++ doesn't allow forward declarations either.
Successfully doing a parse-only on C code doesn't quite work. It turns out the grammar relies on a symbol table. Fortunately, only a symbol table of the typedefs. Once adding that in, ImportC worked. (I really tried to make it work without the typedef symbol table!)
C++ added a bunch more syntax that relies on the symbol table. I would not even try fixing it to work as parse-only.
> in C you don't solve problems by adding features, but by writing more code in C
The trouble with such sayings is like following a google map that says cross this bridge, but wasn't updated with news that the bridge is out.
> Those things aren't that obvious,
They are once you use another language that doesn't have those restrictions.
> and I'd rather not have them added to C.
C adds new things all the time to the Standard, like normalized Unicode identifiers, which are a complete waste of time. Every C compiler also adds a boatload of extensions, some good, some wacky, many ineptly documented, all incompatible with every other C compiler extensions.
Stand-aloneness and single-passness are orthogonal.
> I found no advantage to a single pass compiler. It isn't any faster.
A gigantic advantage: a single-pass-compilable language is simpler. By definition.
Implementations may or may not be simpler or faster.
> C++ doesn't allow forward declarations either.
Well, that's not what I meant.
C++ is "C with just this thing" done way too many times.
> The trouble with such sayings is like following a google map that says cross this bridge, but wasn't updated with news that the bridge is out.
TBH, I didn't really get this. Is this about sticking to C as is, but it is outdated as is?
C would be outdated if it didn't have, say, long long for 64-bit numbers. Having "true" be a keyword instead of a macro doesn't change how outdated it is or isn't, just like compile-time evaluation also doesn't.
> They are once you use another language that doesn't have those restrictions.
I have used many, and I still don't find them obvious.
> C adds new things all the time to the Standard, like normalized Unicode identifiers, which are a complete waste of time.
I agree that many/most are a waste of time, and shouldn't be added to C. The fact of C adding things to the standard all the time shouldn't justify adding even more things, but make one question if those are needed at all, and how to accomplish the goal without it.
> Every C compiler also adds a boatload of extensions, some good, some wacky, many ineptly documented, all incompatible with every other C compiler extensions.
I know about that, and my position is the same: just don't.
I don't use them also.
That's only "by definition" if you take a language that needs multiple passes, then remove the features that need multiple passes, and don't replace them with anything else to compensate.
The "by definition simpler" version of C would not only disallow forward references, it would have no forward declarations either. As-is, forward declarations add some complexity of their own.
(Also, if you can figure out a way to emit jump instructions in a single pass, you can probably figure out a way to call unknown functions in a single pass.)
Doing this with functions is a lot more difficult, because one cannot anticipate the argument types and return types, which downstream influence the code generation. Of course, early C would just assume such forward references had integer arguments and integer types, but that has long since fallen by the wayside.
As is, C already is single-pass compilable, modulo some unnecessary syntax ambiguities.
As the compiler reads the text, it marks some character strings as tokens, these tokens are grouped as a fragment of code, and some fragments of code are turned into machine code. A simple function of a 100 lines doesn't need to be parsed until the end for the compiler to start emitting machine code.
Like the parser, this requires memory to keep tabs of information and doesn't work for all types of constructs, like a jump instruction to a label defined later in a function. The code emitter soaks input untill it is possible, and does so, like when the label is already known and can be jumped to.
Not true.
On the one hand, just see how many non-compiled languages are used outside of primitive school projects.
On the other hand, this simpler approach is actually faster for writing actually fqst compilers. Many modern compiled languages have compilers that work on the order of ~100ms on a simple file with 1k LoC, when it could (and arguably should) work on the order of ~1ms, IOW, imperceptible given the syscalls overhead.
A 100x faster compiler that generates meh code is more useful 99% of the time: when one is recompiling all the time during development.
Firstly, there are at least 3 C compilers in widespread use, from apple, microsoft and gnu, these are a long way from 1 for 1 to each other so when it says for example:
->In other words, while C can compute at compile time a simple expression by constant folding, it cannot execute a function at compile time.
Maybe the compiler he tried cannot, but another can, no idea, it wasnt tested, they can be made to (the whole point of the article), apple and microsoft cannot be made to, everything in this article could have have been submitted as a merge request to gnu.... Article doesnt even state whose C compiler they embedded afaict.
wrt to "standard" c specifically, there are for sure some hard constraints on all the wild and wacky hardware support required that must make proposing and implementing changes within the c standard extremely hard, max respect to the anonymous experts that have got it to where it is today, but imho a lot of the "why doesnt c" questions can be as easily answered as "why doesnt V8 support 8 bit pic micros".
I'm not sure why forward reference declarations is needed nowadays(or if it really is from a language standpoint).
C could probably copy C++'s constexpr & static_assert stuff to get the first 2.
> I'm not sure why forward reference declarations is needed nowadays
The article gives reasons. Although they aren't necessary, they are deleterious to code layout which becomes a slave to the declaration order rather than aesthetic order.
> C++'s constexpr
is still lagging behind D's, after 17 years of development. In D, the garbage collector makes memory allocation in it trivial. Furthermore, only the path taken through a function needs to be CTFE-compatible, the path not taken does not.
https://devblogs.microsoft.com/cppblog/integrating-c-header-...
https://devblogs.microsoft.com/cppblog/integrating-c-header-...
https://devblogs.microsoft.com/cppblog/integrating-c-header-...
(In the past, there were more legitimate concerns on the ease of implementation. Nowadays, as the article points out, they are pretty moot, other than having to keep backwards-compatibility.)
I'm also rather bothered that on the bit on const execution in the article, there was no discussion on how to deal with functions that may not terminate or take rather long to execute. Especially considering the unit tests motivation, this seems like a rather blaring omission.
> how to deal with functions that may not terminate or take rather long to execute
Control-C, the same as when running any executable that shouldn't be taking that long. It doesn't solve the halting problem :-/
There is Vulkan based modules library.
fmt has modules support.
Me and several others already use modules in some extent.
That is a bit more than nobody.
1. Fix the integer promotion rules. Obeying them as they are now makes code considerably less readable.
2. Choose one of the idiomatic approaches to type punning and make it standard. Having to use memcpy() over and over again is terrible.
3. Make casting a pointer-to-struct to a pointer to its first member supported. Stop leaving it to POSIX.
4. Make the exact-width integer types in stdint.h required. They were brazen enough to require support for long long in C99, so why not?
5. Make integer literals without type suffices be compile-time bignums.
More generally though, it's time to stick a fork in c. To me the only sane ways to use c are as a compilation target or for quick and dirty prototypes.
We can't make c better by adding to it. We need to let it die peacefully so its grandchildren may live.
import std.stdio;
alias string = immutable(char)[]
void main() { bar(foo()); }
void bar(string s) { writeln(s); }
string foo() { return "foo"; }
import std.stdio;
alias string = immutable(char)[];
void main() { bar(foo()); }
void bar(string s) { writeln(s); }
int foo() { return 1; }
Your foo() example above has code which has been changed, rather than "if I append to the source file". (I re-read my prior comment and realized this may not have been clear.)
That a change to code can introduce a bug is something we've all seen. But your prior description is not any kind of change, it was specifically an append. In the context of forward references, I am curious to see something that matched your prior description.
I’m not onboard with significant changes to C but the language will always be around at the interface between hardware and software and probably as the lingua franca for FFI.
Every time you do exploratory work you now have to comment out all the tests that this work breaks because otherwise it won't compile anymore.
That would be even more annoying than Go's stupidly pedantic compiler.
Can't that be an optional thing decided by some compiler flag? I think I remember doing something like that in D.
Unfortunately, ever since golang decided on an autocratic and backwards "there are no warnings, only errors" policy, others have started to sip from the same kool aid jar.
Switches can't seem to figure out that I have a case for every value of the enum I'm switching on, so I need a pointless default: assert(0);
I didn't check if this also breaks me getting warnings if I add new values to the enum but not the switch, but I imagine it does
They have been working on bringing constexpr, which exists in c++, to c. This is essentially a constexpr function.
C is fine without these things
It may not be very hyped but the forum and community is quite active. I don't think it's popularity should stop you from exploring it, it's a fascinating language.
Even Fortran seems to have added object-oriented constructs, all kinds of new types and concurrent and parallel programming
It won't become D and you can probably be fairly sure it won't grow a standard garbage collector and object system.
- better enums (with tagged union)
- compile time type introspection
D does the latter (very well btw), but completely missed the mark with enums
The reason I embarked on D is because C and C++ were too reluctant to move forward.
I just want to take this opportunity to say thank you. While D may not taken up from the rest of the world. It has surely lived on in C, C++ and many other languages. Still wish more people would use Das C.
For example, C++ pivoted to using ranges instead of iterators, and even C# changed their iterators to be like D's ranges (or so I've been told).
For example, D will never have a preprocessor. Or over my dead body :-/
Indeed. Compile time evaluation combined with a preprocessor would make for some serious head scratching when it comes to trusting trust.
Michael!
sometimes parsimony is called for. zig is basically c--+ where the + is the constexpr stuff.
[0] minimally 2019, 3 years in:
Order-independent top level declarations.
Underscores embedded in integer literals. (I stole this idea from Ada, which had been forgotten. Soon after D popularized it, it became standard in other languages.)
Continue or break to labeled loop.
Fixed sizes for ints, longs, etc.
Of course, I don't know if there's a straight line here, and Zig is welcome to use any features from D that they like. But it's just interesting that things innovated in D pop up in subsequent designs.
Perl had this years before D even existed [1]. Given its earlier age and higher reach, it's likely that Perl did more to popularize the idea as well.
> Continue or break to labeled loop.
Also a feature that Perl had years before D's existence [2].
These two are the ones I immediately recognized because of my familiarity with Perl, but given the trend, I'm doubtful of the other claims as well now.
[1] https://perldoc.perl.org/5.005/perldata [2] https://perldoc.perl.org/5.005/perlsyn#Loop-Control
I accept that Metaware and Perl did this before D. But I still claim that adoption of it in other languages came shortly after I popularized it in D, as I included it in many presentations about it.
Possibly also taken from Ada, as other text in that section of the manual reference Ada.
See A.3 pg 169 (and 58+) of 235 in: https://bitsavers.org/pdf/metaware/High_C_Language_Reference...
$ a68g --strict -e '(INT a = 1 000; print((a,newline)) )'
+1000
Javascript has had this for functions since 1995. This has been part of zig from the start, not added later.
> Fixed sizes for ints, longs, etc.
this has existed in stdint.h since C99. It doesn't take a genius, only years of pain with C/C++, to realize this is the better way to do things. And also, this was in zig from the start, not added later.
> Underscores embedded in integer literals
Also in zig from the start, not added later. Others have commented on the provenance.
I could be convinced that continue/break to labels was inspired by D.
Hasn't Java had that since the beginning?
rummaging around in my grammar folder...
BreakStatement ::= "break" [ IDENTIFIER ] ';'
ContinueStatement ::= "continue" [ IDENTIFIER ] ';'
Zig is young, and far from 1.0, and many long promised features still not implemented
name one that isn't async / sane recursion (which is also async)
Constexpr function evaluation sounds like a great idea until you start trying to use it, and get surprised when seemingly-constexpr-safe functions aren't constexpr. Or, you tweak one function and suddenly all your fancy compile-time unit tests explode.
Ok, so you get around that with good code hygiene and by limiting the complexity of your constexpr functions... in other words, do the exact things we already do with preprocessor macros.
Alternatively, you add a constexpr keyword to the lang, but now we have red functions and blue functions. Great.
In another language, there'd still be an argument for the type-safety that would precipitate from constexpr function eval, but this is C we're talking about.
How about container_of? Could we please standardize that already? Why is this crucial and immensely useful macro a thing we all copy-paste from that one page on kernel.org?
There's really no comparison with preprocessor macros. All the preprocessor can do is trivial expressions with long values. Not even floating point.
> you add a constexpr keyword to the lang, but now we have red functions and blue functions
My proposal (and D) does not require constexpr. The same function can be used at run or compile time. There is no need for that keyword. C++ made a mistake.
I think you're focused on something that D programmers found helpful, rather than focusing squarely on the needs of C programmers. C and D are both good languages. Their use cases can overlap, but frequently don't.
>=70% of the code I write for work is C, as I'm an embedded firmware dev. C meets the very particular needs of bare-metal development, a use case that continues to be underserved by Rust, Zig, and other supposed successors to C. So, I'll be approaching this with a strong bias towards that perspective.
To me, the argument about unit testing rings hollow because of all the other, far more complicated and runtime-subverting things that would also need to become standardized before it would be feasible to unit test C programs without help from the hideous hacks we use today, like CMock. So, all of that isn't doing anything for me.
> My proposal (and D) does not require constexpr. The same function can be used at run or compile time.
Like you, I dislike the constexpr keyword. But, particularly considering your own example of defining an enum value, I don't see how the "implicit const-evaluatable" approach makes my life easier. Calling functions to define an enum's value is cute, but I can't tell you why I'd actually want to do that. You mention that the preprocessor can't handle floats, but, well, neither can enums!
Adding a single printf (or, in my case, kprintf or LOG_DBG or whatever) would become liable to nuke some constant evaluation happening somewhere far up an obscure call chain. The basic reality of C is that you will, at one point or another, encounter a situation where your only debugging tool is print statements (or a single LED). That's the cold reality of C's paper-thin runtime.
So, I really dislike the idea of having a feature that's liable to make your code go "boom" at compile time because you put a print statement in just the wrong spot. Or a write to a memory-mapped register. Or a hard jump into a blob sitting somewhere in memory. Or inline assembly. Or a call to a function that uses any of those things, even once. Even without the keyword, you end up with red functions and blue functions. It's just harder to tell which ones are which.
Defining some const floats? Sure, that's neat. If you could use this feature to define huge matrices of floats, that'd be pretty cool! There's just a boatload of gotchas.
That is hardly the only place that has a constant-expression in the grammar. (BTW, D enums can also be floats, and even string literals!) You could use CTFE to initialize const floating point globals. static_assert also takes a constant-expression.
> There's just a boatload of gotchas.
The D community has 17 years experience with it. It remains an indispensable feature.
As for embedding a printf, that has come up. Recall elsewhere I said that only the path through a function has to be pure for CTFE to work, not the whole function?
int sum(int a, int b) {
int s = a + b;
if (!__ctfe) printf("sum is %d\n", s);
return s;
}
> If you could use this feature to define huge matrices of floats, that'd be pretty cool!
I use it to statically initialize complicated tables at compile time. Before CTFE, I wrote a separate executable that would emit source code with the array initializer. I like the new way mucho bettero.
If you prefer "hideous hacks" (your words!) I won't take that away from you.
It's usually a bad idea, but very feasible
Anyhow, here's the same article:
https://www.digitalmars.com/articles/Cobvious.html
Fun fact: X's article formatter recognizes D code!
I used the https://publish.twitter.com thing against the Xeet, then lifted the first HREF out of the embed goo.
> This page is not supported. > Please visit the author’s profile on the latest version of X to view this content.
I'll be using X more for articles in the future, but will also put them on the dlang.org and digitalmars.com sites.