Whats special about D? why should i learn it?
Stuff that I particularly like.
Assert/Enforce: http://ddili.org/ders/d.en/assert.html , Unit testing: http://ddili.org/ders/d.en/unit_testing.html , Contract programming help: http://ddili.org/ders/d.en/contracts.html, and http://ddili.org/ders/d.en/invariant.html , Scope (love this): http://ddili.org/ders/d.en/scope.html
And the other usuals -- templates, mixins, etc....
BTW, I mostly use D as a better C than as a better C++...
Another good feature:
Interfacing to C is somewhat easy at least for the basics. (I haven't looked at advanced cases yet, but maybe someone else can comment on that.)
https://dlang.org/spec/interfaceToC.html
This is a great feature IMO, because it allows you to (re)use the huge number of existing C libraries out there.
Here is a simple example:
Calling a simple C function from D - strcmp:
https://jugad2.blogspot.in/2016/09/calling-simple-c-function...
There's a handful more small examples of a few things D can easily do, here on my blog:
https://jugad2.blogspot.in/search/label/DLang
(And of course, there are many more at the DLang tour site - https://tour.dlang.org/ )
Also, there are a few good videos about D (alone) and being discussed along with other languages, at my blog's DLang posts link above.
I'll just put some post titles here to give a quick idea:
Simple parallel processing in D with std.parallelism
Using std.datetime.StopWatch to time sections of D code
Read from CSV with D, write to PDF with Python
Command line D utility - find files matching a pattern under a directory
min_fgrep: minimal fgrep command in D
num_cores: find number of cores in your PC's processor
Func-y D + Python pipeline to generate PDF
file_sizes utility in D: print sizes of all files under a directory tree
deltildefiles: D language utility to recursively delete vim backup files
[DLang]: A simple file download utility in D
Getting CPU info with D (the D language)
Porting the text pager from Python to D (DLang)
https://jugad2.blogspot.in/2017/04/porting-text-pager-from-p...
Think C++ template metaprogramming but much, much easier and thus, seemingly more powerful. It's not that you couldn't do the same in C++, but D's metaprogramming is so much more accessible that it makes you want to use it.
You'd probably do large portions of it in "constexpr" types and functions rather than relying on recursive metaprogramming techniques.
They are also planning on adding overloading based on whether a function is constexpr, which is important if you want the same library to support both compile-time and run-time matchers.
So it's all theoretically possible already. But D has the advantage here in that it's not just possible but usable.
Well, imagine that all of the things you can do in Python by messing with dunder methods, function decorators, or metaclasses could be precomputed by a compiler and would not even execute at all during runtime. It makes everything really fast at runtime and easy to precompute at compile time.
Is there anything in D similar to decorators? How does the registration pattern work in D, for instance?
https://github.com/rejectedsoftware/vibe.d/blob/master/examp...
Decorators (in D, 'user defined attributes', or UDA) work differently. It's not a function-composition feature, but more of a tagging feature. You write a class, function, etc., tag it with custom attributes; and then have a separate compile-time function walk over your code, find the decorators, and augment the code based the meaning of the tags. (I used to wish that D had adopted Python-style decorators, since they are easy to reason about and implement, but I can see the logic of the more general UDA system that they adopted.)
In practice, though, you would often use templates to achieve the same effect. Given a memoize template (really, just a memoize function), and an expensive-computation function,
auto fastComputer = memoize!expensiveComputer;
@memoize
def expensiveComputer(): ...
I found that some of the Nim's MP features, in particular AST macros, are a little harder to work with than D's templates and compile-time function evaluation. You get a lot of flexibility, but the cost is high. I'm not a big fan of how "mixin" is used in D to splice source-text into a generated function, it's certainly less principled than an AST transformation, but in practice the resulting code tends to be concise and easily read, whereas the AST-macro approach introduces a lot of accidental "noise" and complexity. The complexity raises the bar for reaching for a compile-time solution, where in D it seems equally as natural to write compile-time code as it does to write regular code. (Not to pick on a strawman, though -- AST macros are not Nim's only MP tool.)
The Nim MP feature I never really played with was the rewrite rules. They seem interesting in theory, but maybe a little too magical for my liking!
I have a lot of respect for Nim. I am glad we live in a world with so many options. Like Walter said in an earlier comment, it's an embarrassment of riches. :)
Can you elaborate on how D is planning to sort out the garbage collection? Nim's GC is extremely fast and thread local, and can be disabled without breaking libraries (according to the author, it does something with memory regions that I haven't 100% grasped yet).
I've googled about D's garbage collector and it's apparently been discussed as the language's biggest flaw since 2013, but I can't find any information whatsoever on what's being done in that regard.
The collector itself isn't being improved as far as I know -- at least I haven't seen any initiatives mentioned recently with that goal. In fairness, I haven't been following the community activity very closely in the past few months, but I think that's accurate. Nim definitely has a technical advantage re: its GC implementation.
The bigger movement has been the "@nogc initiative", which started with adding a @nogc attribute to the language (the compiler can verify that a function tagged with @nogc, and all of its callees, do not allocate GC memory). There is an ongoing initiative to make more of the Phobos library @nogc-compliant, to take advantage of this feature. There has also been a lot of work on custom memory-allocators [1], and I think the plan is to incorporate into Phobos where it makes sense, so you can have functions which take custom allocators, have thread-local allocators, etc.
https://dlang.org/phobos/std_experimental_allocator.html
I don't speak for the community or the dev team, but I think the long-term goal is to make the GC a feature that is available when you want it, but that isn't a dependency for using the standard library. Either through custom allocators or through @nogc guarantees, you'll be able to ensure that your program's memory management is deterministic.
For anyone else who's evaluating D and looking into its GC situation, the most recent blog post on Dlang.org (https://dlang.org/blog/2017/03/20/dont-fear-the-reaper/) seems to embrace the presence of the GC, but also ends by saying the next blog post will describe how to go without the GC. So there is indeed awareness/activity on that front!
(If I'm going to learn a new system programming language, which one should I pick?)
I would say that I have found it to be more of a problem on Windows. That'd because the general C/C++ package management solution on Windows is quite... Old fashioned, and that's not always a D specific problem.
I REALLY ENJOYED D1, REALLY! (CAPS 11). D1 was like C, but better. It was heavenly. D2 is like C++, but better. Not my cup of tea though. Give it a spin for a day or two. I'm sure you'll like it if you like C++. Trouble arises, as with all niche languages, when you try to move to production and you have to source libraries and/or support.
Rust is newer (though being used in some big projects like Firefox/Servo, Visual Studio Code's search functionality now uses it by default, etc), has (afaiu) a more powerful type system, and is entirely memory-safe by default. However, this makes it somewhat harder to learn at first, and it also has a relatively slow compiler. It follows ML-style languages a bit more, with things like pattern matching and sum types built into the language.
Personally, I prefer Rust, because it feels like a stronger foundation with the ML-like type system and no GC. YMMV though, depending on what is important to you.
I guess your original comment was maybe meaning how D enforces (the "normal" definition of) memory safety differs to Rust? In any case, I read over both of those, and, to me, they both seem to essentially be a slightly less general version of Rust's scheme (possibly independently invented), rather than something very different. I'm interested to hear how you think they specifically differ to Rust.
There's no notion of "borrowing" in D nor any notion of "only one mutable access at a time".
Well… it's relatively slow in release mode, but C++ compilers can often be slower. GHC is always slower :D
In other words, if you're looking to replace/supplement your C use: go Rust. If you're looking to replace/supplement your C++ use: probably go D, with some caveats towards actual use.
Note: I like both languages, but do prefer Rust for my personal use cases.
Some details here... every language other than assembly languages has some amount of runtime. This is Rust's: https://github.com/rust-lang/rust/blob/master/src/libstd/rt.... (as you allude to, many people refer to this amount of runtime as "no runtime" since it's very, very small.)
You could also consider some other things as part of a runtime; for example, by default on most platforms, Rust includes jemalloc. That can be removed, though not in stable Rust. Same with the standard library code, which can be removed for libraries, but not binaries just yet (due to a small technicality regarding the stability of some attributes.) Things that do this are likely to use some of Rust's other unstable features at the moment, so it's not generally a burden to do so, and those interfaces rarely change right now.
How are you defining "runtime" such that this statement is correct?
I see a distinction between a runtime library and a language runtime. The former is just a set of convenient routines for interacting with a specific platform. The latter is something that runs alongside your program to facilitate its execution, like a JIT or an interpreter.
The key is, you are doing the injecting in asm.
Anyway, your distinction is pretty solid. Most people just use "runtime" to mean either one, and then rely on the context to disambiguate.
In short, I thought Rust was "we solved the pain of this difficult thing." However, it is not really a novel solution to the difficult thing, but simply a decision to undertake it.
I've now moved to evaluating Nim and D, and while I've barely dabbled in them (mostly going through the docs and writing some simple example-like code), I can at least say that Rust is likely to be much more controversial and polarizing than these languages. I recommend giving it a try - go through the official "book" which serves as the main documentation. If you survive lifetime annotations without finding them too obnoxious, then you'll probably like Rust.
Personally, I find Rust's extreme rigorousness (and the laboriousness that follows from that) makes it very niche, and I find myself rather unexcited about using it for anything.
The annotations have, for the most part, faded into the background for me. I don't find them to be particularly pervasive in the code I write, and when I do need them, it's usually to fix a reasonably straight-forward case where the compiler failed to elide them. With that said, in the years I've been using Rust, I have committed one or two lifetime-related bugs. (No memory unsafety resulted, of course, but it did result in data being annotated with a shorter-than-actual lifetime.)
> In short, I thought Rust was "we solved the pain of this difficult thing."
Part of the pain that Rust purports to solve is the significant reduction (and debugging thereof) of memory unsafety errors. In return, you must deal with the pain of an ownership and borrowing system, which might present challenges to patterns you may have used in another language. The benefit is that you have a compiler to tell you when you've mis-stepped instead of an end user filing a bug report (or worse).
Other than lifetime annotations, I have a couple other niggling issues with it but I suspect it's because I haven't fully grasped certain things yet, and so I'll refrain from commenting on them for the moment.