If x - (fast_dev_time + ease_of_learning + common_runtime + managed_GC + easy_of_understanding) = kicks_ass, then what's x?
In other words, what redeems C++? What's the point of the language?
In other words, what redeems C++? What's the point of the language?
The question to ask is:
- do you just care about results: I need a program that produces these outputs when given these inputs
- or do you care about what actually happens: I want the computer to do this, then this, then this, in exactly this way please.
...?
It's usually a good idea only to care about the former -- the essence of functional programming, higher-order functions, etc., is to be able to focus on the former as much as possible -- and so long as you only care about the former C++ doesn't have much to recommend it except in special circumstances.
On the other hand, there are times when what happens, exactly is important (eg: device drivers, other low-level code, directly interacting with hardware, etc.). In that scenario what C++ offers is a language that standardizes a lot of the functionality that most sufficiently-large raw-C programs have implemented in an ad-hoc basis.
There are other ways of doing low-level code, but at the present time C++ is the best of bunch (or at least the safest choice if you have an eye to the long term), not so much b/c it's particularly awesome but b/c the others have either faded away for business or political reasons, or b/c the others made limiting choices (C++ makes very few decisions for you, which means it's equally suited -- or unsuited -- to every task in its particularly niche).
On top of that, C++ has damn powerful meta-language facilities no other language of any level has, which are, however, beneficial only when in good hands. It's too easy to misuse C++ unfortunately.
However, I'll have to very strongly disagree with "C++ has damn powerful meta-language facilities no other language of any level has". C++ actually has terrible support for meta-language facilities.
It is inconceivable in my mind that C++'s support for that is anywhere near something like Common Lisp, so forget about it being the best in that respect. I'd love to know what parts of C++ are great meta-language facilities. If you say C++ macros I'll have to laugh. Hard.
</smuglispweenie>
e.g., http://www.antiquark.com/escape/public_html/stepanovusa.html
There are various gnarly problems with C++'s model, some of which show up as gnarly problems in STL, even in fundamental stuff like implementing collections of refcounting pointers last time I looked. But as far as I can tell, every language which tries to get this correct within the language has some serious limitations or issues, arguably at least as bad, especially if like Stepanov one of your top priorities is eliminating every last bit of runtime overhead in the generated code. (E.g., implementing arrays of objects only as arrays of fixed-size pointers into variable-sized objects on the heap, as in typical CL and Java, is a no-go given STL priorities, and thus STL constantly wrestles with a bunch of problems that lots of other implementors have dodged by giving up on them.) As far as I know, no one has a comprehensively satisfactory solution for metalanguage facilities within the language.
Getting metalanguage correct by stepping outside the language and upstream from the compiler, writing a separate program to generate the target program, has been a solved problem as long as we've known how to write compilers in Turing-complete languages. That approach is sometimes used for app code in conventional languages, as in FFTW, and to some extent it's what Lispy macros do. But for some applications, including STL as I understand it, stepping upstream is unsatisfactory. Sometimes what you'd really like to do is have your code generator query the compiler about what the compiler knows. STL in particular, IIRC, wants to have its code generation depend on what the compiler knows about types and typedefs and so forth. In an ideal world it would be routine for code generators to be able to ask the compiler about other things, too, like dead code, namespaces, and safety and other pragmas.
Umm, lisp macros can implement all of C++ meta-language facilities and more, so how are said meta-language facilities more powerful?
And then there's the meta-language protocol....
{
X x, y;
if (x > y)
return;
// some code ...
}
http://www.ai.mit.edu/projects/iiip/doc/CommonLISP/HyperSpec...
There's a reason why PG refers to non-lisps as "blub".
http://www.gigamonkeys.com/book/beyond-exception-handling-co... http://www.lisp.org/mop/index.html
C++ destructors are a powerful tool, you can create data types that otherwise would require support on the compiler's side.
You're right - they're more powerful, but bringing that up didn't seem necessary.
> And no, it's not necessarily memory clean-up, of course.
Never said that they were. However, C++ programmers spend a fair amount of time worrying about/writing code for memory cleanup and destructors is where a lot of that time/code goes.
Folks using languages with GC don't do that nearly as much.
Destructructors are only implied for scope-allocated variables. By tying value lifetime to variable scope, C++ gets to do certain things, but as a result, programmers have to do certain work.
Lisp values are not tied to variable scope, so complaining that lisp doesn't have mechanisms for values that are tied to scope is sort of like complaining that a hovercraft doesn't have a parking brake.
> C++ destructors are a powerful tool, you can create data types that otherwise would require support on the compiler's side.
Actually, they're just a mechanism for calling code when a value "goes away". That's almost required for a language with manual memory management but unnecessary for languages with GC.
However, destructors are also the only way that C++ has for automatically calling code. Other languages have other, more general, mechanisms.
So, languages that provide no way of controlling allocation have relatively limited application compared to those that do provide full control over memory allocation.
By "relatively limited" I mean just relatively, that is, the reason Python, Ruby, Perl, PHP, Java, C# and Lisp with their GC facility exist is that it works most of the time, but there are certain areas where you have no choice other than C/C++. Kernels, compilers (including Lisp compilers), game engines, everything that deals with hardware, image, audio and video processing, etc etc.
This is an endless list where you really have no choice. Try to write a VST plug-in in Lisp, for example, that would add a reverb and will be able to do it on 8 audio channels in real-time on a 3GHz CPU.
Wrong
> They are fine in some situations, but may turn to a problem in others.
Correct.
> For example, you may get very undesirable effects if you are creating and destroying a large number of objects in a time-critical application (a game, etc).
Not if you're using a reasonable real-time GC.
If allocation and reuse is occuring, memory management code is being executed.
GCs tend to run a bit slower, but you get faster development. Sometimes that's a good trade, and sometimes it isn't. (My real-time friends are correct when they say that late answers are wrong answers. However, it's also true that wrong answers are wrong answers.)
> compilers (including Lisp compilers)
Wrong again.
> everything that deals with hardware, image, audio and video processing
Wrong again. (Yes, lots of such systems are built with C/C++ but folks have done them with GC languages.)
And, our python friends have figured out that one can use C/C++ as an extension language for the heavy processing, where very little memory management occurs, and python everywhere else, getting the benefit of both worlds.
This is important because, when you get down to it, most of the applications that have lots of signal processing and the like are actually a couple of time-critical small kernels surrounded by lots of other code. Said other code dominates development time so GC for it is a big win.
> game engines
Yes and no, because "game engine" covers a wide range of things (from physics and rendering through high level "AI") and it depends on the available processing power.
One interesting thing about the "performance is everything" crowd is how many of them use gcc even though there are other compilers for many ISAs that deliver significantly better performance.
Where exactly did PG say that all non-Lisps are "blub", whatever that means?
C++ is a fickle beast, but it is powerful and expressive. Like the grandparent, given that C++ is my best language, I do genuinely enjoy working in it when the situation fits.
For all of the talk of succinctness of Ruby, et al., I've had to rewrite a handful of Ruby lately in C++ for performance reasons and with a reasonable toolkit (e.g. Qt) really it wasn't much more code to get it done in C++ (about 30% more), for a runtime boost of about 1500%.
Qt's meta-object-compiler also adds things like introspection and call-by-name to QObject subclasses enabling some powerful things more typical of dynamic languages.
Granted, the real danger is that it blows up in the hands of someone not used to it, but it's a nice tool to have in your bag-o-tricks.
But 99% of my life can be managed just fine with addition, subtraction, multiplication, and division.
It's that other 1%, though, where more advanced math kicks ass. If you've never seen it or watch it happen it's hard to describe how cool it is. With C++ you're controlling the CPU at a level just above machine language.
I love advanced math, but I rarely ever use it. Advanced math kicks ass.
I think C++ does a decent job of being as logically expressive as practical while still supporting C-level memory micromanagement. Typically exposing C-level memory micromanagement issues is a bug, but occasionally it's a feature. So to me, the point of C++ is to express abstractions like polymorphism and exceptions in the same few pages of code as low level memory operations. How often do I want to do that? Not very often, but it can happen.
Also, while C++ is very hairy and I wouldn't want to have to implement it, C++ seems to be implementable enough and standard enough that it may be usefully supported on a platform well before other more expressive languages. Perhaps it's because a lot of the C++ hair is frontend target-independent stuff like parsing and templates, so that once you've ported the C backend you're almost done porting C++ too? Dunno for sure why, but it seems to happen: e.g., it was my impression on my Atari ST many many years ago, and is my casual impression that something similar happened for the Arduino more recently.
C++ is admittedly a weird mess in various ways, but given the choice of source almost-compatibility with C (which I don't particularly value, but which I can at least understand) and C-level linkers (which I have mixed feelings about) a mess seems inevitable. Thus, I still consider it an impressive design.
Occsionally I've seen IMO-excessively broad claims that higher level languages are the best. It sometimes makes me think I might be able to cook up an example where C++ would be hard to beat: a small backtracking search problem where trailing operations (in the sense of "trailing" that you'll see if you Google "trailing backtracking") are in the inner loop. Take this thought of mine with a generous amount of salt, because I've never boiled it down to a really clean challenge. OTOH, I have at least implemented such search in several languages, and I even did a few casual benchmarks --- but 10+ years ago, when performance tradeoffs were rather different.
That's a particular case of a general theme where C-level programming could win: performance dominated by a very simple memory allocation regularity (LIFO, in this case) that the GC doesn't know about. (This theme also involves the precondition that you should care more about a factor of 2 in performance than a factor of 2 in programmer time, which often doesn't hold.) In many instances of this theme, the accreted featuritis bloat of C++ would be overkill, so you'd prefer C. In this instance, though, placement new() of polymorphic objects into LIFO-allocated raw memory is more expressive than anything I can see how to do in C.
Now, we should not forget that many programmers can go all year without running into a single problem where a factor of 2 in performance is worth a factor of 2 in programmer time. And we should not forget that even the ones who need to care deeply about performance often find it's not determined by a few low-level hotspots where low-level tweaking helps. But in some subfields, it's not too unusual to rationally choose to micromanage stuff at the level of C/C++. (I nominate the subfields of embedded programming and compute-heavy search from personal experience, and Quake/Unreal-like engine programming by reputation; I also explicitly do not nominate implementing web browsers, ow ow ow.)
It's harder to think of reasons I'd choose to write sizable programs in C++ (other than the compelling but unsatisfying accidental-seeming reason of early availability on a platform). One reason, though, is that there are many subproblems for which the choice of language doesn't matter all that much. E.g., Fortran is adequately expressive for a lot of the stuff in a book like _Numerical Recipes_, and you can famously write Fortran in (almost) any language. Because of this, I sometimes encounter a program where some key subproblem really cries for a particular style of language, possibly C++, and then I can be language-agnostic about solving the other subproblems, not minding writing it in whatever language I chose for the key part.
It's a drop-in replacement for C that is much more powerful and succinct.
That said, C++ is in no way a "drop-in replacement" for C. What makes C++ "interesting" is that most of the time, you can drop C code into a C++ program and it will just work. Of course, you can do the same thing with Objective C, and the object model behind Objective C is much more sane.
I'm shocked you're saying this in seriousness. C is a simple language lacking a large number of constructs and compiler safety features of C++. You might as well argue that BASIC is just as powerful as Python.
Inherently OOP problems like large simulations with huge class hierarchies could not realistically be done in C. The C++ frameworks for writing servers have no parallel in C because the language lacks required abstractions.
I have never seen C code that could not be rewritten more clearly in C++.
Templates, while useful and (sometimes) fun (as long as you're not having to debug them), aren't as interesting as having a real dynamic language like Python or Ruby.
I'd argue that your statement about "Inherently OOP problems" is incorrect from the first word. IMO, there's no such thing as a problem that's "inherently OOP"; there are problems which may be modeled easier in OO, but there's no problem that OOP solves that can't be solved a different way. (Why does a large simulation require a huge class hierarchy in any case? Maybe you're just Doing It Wrong.) There's also an assumption that C can't do OO, which is patently false; it's just not sugared for you like in C++.
I'd love to see what "required abstractions" you think that C++ provides, because I just simply don't see them. Except maybe namespaces. Overloading is nice, but not a necessary condition. References are just a mess. Templates are overkill for a lot of things. RTTI in C++ is a joke, especially if you're working cross-platform (and dynamic_cast on older versions of g++ just don't work, and sometimes you just can't escape those older versions).
All that said, I write C++ in my day job. A lot of it. But I don't pretend that anything I'm doing in C++ couldn't be done in C, possibly better and cleaner. We're designing a new set of APIs for plug-ins in our product, and we're moving toward a clean set of C-based APIs because they're (a) more portable across platforms and (b) more portable across languages so that we don't force people who want to write plug-ins for our product to use C++.