GCC 4.8 Has Automatic Return Type Deduction(yapb-soc.blogspot.ru)

41 pointsby AndreyKarpov14 anni fa48 comments

yapb-soc.blogspot.ru

GCC 4.8 Has Automatic Return Type Deduction

http://yapb-soc.blogspot.ru/2012/12/gcc-48-has-automatic-return-type.html

6 comments

ebassi14 anni fa

a three lines program generates 95 lines of error messages; let's throw a template into it, so that it goes up to 112 lines, but look: at the beginning you'll see the error we added!

coupled with the: "To be fair, this doesn't entirely replace decltype. auto doesn't perfect forward. But it seems to work as expected, most of the time" it goes a great way to instil me a sense of safety.

not.

that post should be taken as an example of why C++ has become a liability, and the day won't come too soon when this joke on the whole industry finally gets dumped like COBOL in the nearest ditch, along with the corpses of all the projects that made the mistake of actually using it.

if it were a living thing, I'd shoot C++ in the face to put it out of its misery.

verroq14 anni fa

I don't get all this C++ hate from people that has never even used it.

Personally I want a better C and C++ satisfies most of what I want.

    1. Type level polymorphism (generics/templates/etc)
    2. Easier ways to manage memory (constructors/destructors, auto/shared pointers)
    3. A modules system (namespaces)
    4. Lambdas, etc to make life easier (C++11)
    5. A standard library with useful data structures
    6. Fast

It seems all to me all these haters still think that C++ is just C with classes, but C++ is a fairly vast language and OOP is just a small part.

C++ is blazing fast, it has an elegant standard library and templates do make sense if you know what you are doing.

You are trying to use cutting edge features that aren't properly standardised yet and complain that the error message is a bit long? Granted, template error messages aren't always the one liner you are expecting, but they are readable.

ebassi14 anni fa

> I don't get all this C++ hate from people that has never even used it.

wrong. I use it every day, on a fairly large code base.

obviously, for portability reasons, nobody working on the project is allowed to even think about C++11, as well as other headache-inducing features - and that includes a fair chunk of the standard library.

gurkendoktor14 anni fa

> a three lines program generates 95 lines of error messages; let's throw a template into it, so that it goes up to 112 lines, but look: at the beginning you'll see the error we added!

95 lines of error messages sounds terrible, no doubt. But which language is better in the real world? I am currently consuming a JSON web service written in Java, and I get no less than 30kb of stack trace back when something blows up. Rails' stack traces are filtered by default, but sometimes you still have to jump in there.

And C++ has the advantage that much of this can happen at compile-time.

I agree that almost everything about C++ is broken, but the verbosity of error messages is the smallest of it IMHO.

raverbashing14 anni fa

I'm thinking most of the "C++ school" is affected by excesses, still, Java and C# are slightly better

" but the verbosity of error messages is the smallest of it IMHO"

It's merely a consequence of the verbosity/complexity of the language itself

wladimir14 anni fa

I read that blog a bit and it seems to have the following pattern overall: elegant 5-line Haskell program. Then follows 100-line unreadable C++ implementation. My conclusion is that C++ is a very bad language to try to do Haskell :-)

This doesn't mean that C++ doesn't have its uses, but for your sanity's sake don't use it for high-level metaprogramming.

stingraycharles14 anni fa

The issue you describe is more a compiler-specific issue than a language specific issue. Yes, the language allows a lot of flexibility and therefor in some situations it's hard to nail down an error to a nice, specific error message (mostly when templates are involved), but it's not impossible, as clang++ shows.

Believe it or not, there are people (like me) who actually enjoy coding in C++.

fafner14 anni fa

It's a language specific issue. Sure clang++ has improved error reporting and GCC is actually quickly catching up. But the problem is a language issue because an error in a template confronts you with implementation details of the template. There is nothing the compiler can do about it.

shin_lao14 anni fa

Or you can use Clang.

Feel free to shoot C++ in the face. Don't forget to rewrite most of compilers and operating systems in use in the process.

microtonal14 anni fa

Except that clang++ is only marginally better. E.g. trying to copy a std::copy a string vector in a size_t vector will give you this beauty:

http://pastebin.com/H68j6E50

Cascade a bunch of errors, end you'll soon be writing a script to analyse error output ;).

fafner14 anni fa

Clang is not the solution. Yes it has some better error messages. Although GCC is quickly catching up.

But it can't solve the core problem. It's simply the language. The lack of Concepts (or something similar) means that error messages simply refer to implementation internals of the Template you are using. Easily giving you a long cascade of error messages when it's in some Template that is used by the Template.

All of the sudden you have to look at implementation details of your standard library or something even worse such as boost. Just to figure out what the mistake was.

And there is nothing Clang or GCC can do about it.

bhaak14 anni fa

Linux doesn't use C++ and AFAIK the BSDs also don't.

So go ahead, I won't have a problem with a dead C++. :-)

verroq14 anni fa

Then prepare to drop GCC. Then drop whatever browser you are using and most of the cross platform compatible GUI frameworks (GTK, QT etc).

https://lwn.net/Articles/390016/

bratsche14 anni fa

GTK is written in C, not C++.

verroq14 anni fa

Sorry was thinking of something else.

wolf550e14 anni fa

There is much more to the OS than the kernel. Lots of important software is written in C++.

indeyets14 anni fa

that's not a problem in the long-term perspective as it doesn't force anyone else to use C++

abrahamsen14 anni fa

What would the clang error message be?

btn14 anni fa

It's roughly the same as the improved GCC error message ("index out of range"), but with only 29 extra lines of incomprehensible compiler meandering and stdlib internals!

neumann_alfred14 anni fa

projects that made the mistake of actually using it

You mean stuff like Unreal Engine... ?

coliveira14 anni fa

What many people don't understand is that C++ has at least two target audiences: (1) people writing low level libraries using templates and other esoteric stuff; and (2) people writing application code. (1) is needed because C++ is a language that can target multiple environments and operating systems. The template craziness is necessary to make the system fast and easy to use for application developers. If you are writing applications, however, you should try to use only bread and butter features, along with standard libraries such as STL and semi-standard stuff like Qt. Once you understand this, your life will be much easier with C++.

indeyets14 anni fa

I used to be c++ "guru" some years ago, but right now code like this scares me as hell. The language is getting less-used and it's a good thing http://www.tiobe.com/index.php/paperinfo/tpci/C__.html

How many years would you give it to stay ubiquitous? I bet on 15 years

udp14 anni fa

I was just about to make a similar comment. There isn't much about C++98 I don't know, but having ignored C++11 for too long I feel utterly lost looking at stuff like this now.

What concerns me even more is that it must be pretty much impossible for a beginner to pick up C++ today.

fafner14 anni fa

> What concerns me even more is that it must be pretty much impossible for a beginner to pick up C++ today.

There certainly are issues when learning C++. But I don't think it's impossible. A major concern is the fact that there was never a centralised website collecting good information and filtering out the crap. There never was a central Tutorial or Reference.

All the knowledge is hidden in very expensive books and worst of all there are many publishers simply spitting out piles of bad C++ books.

http://isocpp.org/ and http://en.cppreference.com/w/ are a huge improvement.

Stroustrup's book is a great introduction: http://www.stroustrup.com/Programming/ I wish he'd made it freely available. A lot of programming beginners aren't happy to pay $50-$70 for a book when they can go to other languages offering great beginner tutorials for free.

And C++11 is pretty new. So of course there is a transition period with books, articles, references catching on.

pjmlp14 anni fa

Anyone can pick it up if they really care.

They don't need to know the complete language on day 1.

fceccon14 anni fa

As a beginner programmer (a.k.a. CS student) I was able to pickup the basic of the language in the last 2 months and work on a real world (not a school project, it's a library that other universities use) cuda c++ project. I read a book so I have an idea of what can and can't be done, but when I need to implement something unusual (ie function object) I need to lookup it in the book or ask for help to my mentor. I still need help to understand gcc errors, cuda uses an "old" version (3.4 I think) so we don't get the improvements of the new versions.

pjmlp14 anni fa

Yes, you always need to look things up.

In the projects I take part on, with teams from 20 - 100 developers, you cannot know everything regardless of the language.

pjmlp14 anni fa

I am still waiting to see a language that can fully replace it.

indeyets14 anni fa

I'm not sure that's needed. It would be much better if parts of it are replaced by different languages (and that's exactly what's happening)

haskell, python, erlang, clojure, scala, d, go, lua… take the tasks one by one. the glue is C (but something like llvm-assembly might take it's place eventually)

pjmlp14 anni fa

A language able to do multi-paradigm programming while giving the ability to do low level stuff as well as high level programming, while compiling to native code.

I really miss the ability to compile to native code in most implementations for mainstream languages nowadays.

I am looking forward to D and Rust, but it will take ages before any of them really get into mainstream.

C, well I haven't touched it since 2001.

lmm14 anni fa

>I really miss the ability to compile to native code in most implementations for mainstream languages nowadays.

What's your use case for it? Is it covered by .net's (often overlooked) native compilation capabilities?

pjmlp14 anni fa

True, but it is one specific case and not multi-platform (Mono does not run everywhere where C++ does).

If you need to make C# work in all scenarios C++ is used, then a compiler with static linkage is also required for scenarios where deploying CLR is not possible. A compiler like Bartok.

Specially if you would like to replace C++ everywhere where it is being used.

So I've learned to make use of "Worse is better" philosophy and keep using C++ for my native code needs.

lmm14 anni fa

Can you give specific use cases? Obviously there are some things that need e.g. manual memory management, but my instinct is that situations where you need to have the same module do both that and use high-level C++ features are vanishingly rare. So I'd be inclined to replace C++ with C in a few cases and a high-level languages in other cases.

pjmlp14 anni fa

- Games

- Systems programming

- Compiler development

- Being able to deliver an application without depending on a VM

lmm14 anni fa

- Games

Maybe. I'm currently playing lots of Kerbal Space Program, and didn't even realise it was written in C# (well, I noticed how hot it makes my laptop).

I can see for something like an FPS engine you'd want as much performance as possible, but doesn't that mean C (and increasingly CUDA and friends)? Similarly big physics number-crunching tends to be in fortran, sometimes with python to glue it together.

- Systems programming

As in kernels? Linux famously uses pure C.

- Compiler development

Does that need to be C++? I believe most if not all of the Java compiler is written in Java.

- Being able to deliver an application without depending on a VM

Why would that ever be a requirement? What's the difference between a VM and a runtime library (which even C has)?

C++ might sometimes be the best choice, but I don't think it's the only option for any of these cases.

pjmlp14 anni fa

> well, I noticed how hot it makes my laptop

That says it all

> Does that need to be C++? I believe most if not all of the Java compiler is written in Java.

Depends which compiler you mean. Oracle's is a mix of C++ and Java.

> Why would that ever be a requirement? What's the difference between a VM and a runtime library (which even C has)?

They are not several megabytes in size.

You seem to like C, fine for you.

I won't touch C again unless one of my customers requests me to.

Clang, GCC already moved to C++.

Haiku, Symbian, z/OS, Mac OS X drivers and many parts of Windows kernel are written in C++.

greyfade14 anni fa

Haiku is written in C++ because BeOS 5 was written in C++, using the GCC-2.95 compiler. BeOS used C++ because when it was written, C++ was the new trendy OOP language. They use GCC-2.95 because the GCC 2.96 compiler was badly broken and GCC 3.x changed the ABI. The dialect of C++ supported by GCC-2.95 is based on extensions to C++98 that were rather quite buggy. It's a bit of a mess, and I would hardly hold it up as a positive example of C++ in use.

Similarly, Windows was written primarily in C, as it predated C++. Their compiler was extremely buggy and had only partial support of features in C++98, so the vast majority of the code in Windows is C with Classes. (Unless there's been a lot of rewritten code in the last 15 years or so.) Again, not exactly a positive example.

nicholassmith14 anni fa

You know when you get in a really fancy sports car and sit down and look at the console and go "What the fuck?" as your brain tries to parse the myriad of options relating to everything that are usually highly non-intuitive and often buried under many layers of cruft and you need to sit and read the manual that's as thick as a phone book? That's kind of what C++ is getting towards.

There's a simple solution, don't touch all the fancy and extreme language features, use the core, keep your sanity. I code in C++ professionally using Qt, the last time I wrote any code using anything overly fancy was probably when I was in University. It's often not needed, it's guaranteed to make your code base a nightmare, and it's usually horrid to read back over. If you're sensible and put some constraints on what you're doing C++ is a great language choice, but often people stray into using all these areas of C++ that basically make the code an unmaintainable mess.

(note, defining core as the things guaranteed to work on 95%+ of current compilers, if it's non-standard I would really, really thing twice about using it)

kombine14 anni fa

It'll take years before it becomes part of the spec and all other implementations will catch up. D had it for ages.

[deleted]14 anni fa

(1)

rbanffy14 anni fa

I'm curious: how popular is it to use syntax that's not available in other compilers and how often do programmers regret the decision?

mdonohue14 anni fa

Coverity, maker of c++ static analysis software, and where I used to work, has published a paper about their experience trying to parse customer code. It turns out that 'The language people code in? The strings their compiler accepts'

So yes, it is quite common to use syntax not available in other compilers. Most code is vetted against only one compiler to begin with.

http://www.stanford.edu/~engler/BLOC-coverity.pdf

fafner14 anni fa

Do you use EDG or another frontend? I can only assume that parsing C++ is quite problematic especially with all those compiler extensions and the current transition to C++11.

splinterofchaos14 anni fa

This particular feature isn't offered by anyone else, so I would not write a program with it and force anyone else who wanted to compile the code to use an unsupported, bleeding edge version of GCC. But I /will/ create a branch of a project or two, using this auto deduction, and send bug reports back if necessary.

I, and many others, have been writing code in Clang and GCC for years that could not be compiled in MSVC. But that code was standard c++11. This is experimental and people should be aware of that while using it.

Someone14 anni fa

In my (limited) experience, it is not that popular, compared to the use of semantics not available elsewhere (is char signed? Can you cast a void* to int and back without data loss? What happens when you right shift a signed int? etc) and to the extreme use of third party libraries (why the #%$! do I need that GUI library in this json parser? Half an hour later: oh, so it is only for these three typedefs, a few macros, and this convenience debugging function), but it surely does happen.

I also think programmers do regret the decision. Unfortunately, that is unlikely to change, as the programmers regretting the decision almost always are not the ones who wrote the software. It is way rarer for a code base to move compilers within a project/team than for a team wanting to incorporate a third party library into their codebase/compiler.

stingraycharles14 anni fa

It depends on your environment. If you completely control all the environments your application is deployed in (for example, when you provide a SaaS), it's fairly common.

dagw14 anni fa

I wonder how many times programmers are even aware that they're using syntax not available in other compilers. I remember the first time I used a non-gcc C compiler and was greatly surprised that things I'd taken for granted and simply assumed was 'C' didn't work.