C++20, How Hard Could It Be • Hacker News Board

Re: C++20, How Hard Could It Be

#121

Post by pjmlp » Sun, Sep 25, 2022, 1:34 PM UTC

hi_herbert wrote: post #83

pjmlp wrote: post #52

Earlier quoted context omitted.

Except Visual C++ already has those ideas implemented, so.... Even exported templates, as hard as they were, the EDG folks actually implemented them, only others decided not to follow upon. The current state with clang is a mix of MIT like license, and those that profit from it not caring about upstream, even GCC is doing better.

I'm pretty sure this rethoric is fallacious, most VMs/languages are not GPL and have MIT-like licenses and yet do not have the issue. It's just that clang lack human resources. Compagnies are not really secretly maintaining their own fork of clang with full support for modern c++. It's not in their economic interest to have to fo all tjis engineering. Instead of malice it'd just plain mediocrity. Yes there are trilli…

The facto only for FOSS systems I guess.

Re: C++20, How Hard Could It Be

#122

Post by pjmlp » Sun, Sep 25, 2022, 1:36 PM UTC

loxias wrote: post #62

otabdeveloper4 wrote: post #28

Earlier quoted context omitted.

gcc is better than clang on every metric. Sorry, it's the facts. ¯\_(ツ)_/¯

Whoa, really? Since when?? After a lifetime of using GCC, I (like many others) moved to clang a few years ago, out of frustration with the slow development of GCC, a desire to use new C++ features, and stayed because of the superior error messages and, in my use cases anyway, superior code generation. In addition, I gather it's a much cleaner and easier to maintain code base. As a result, we get to have cool things l…

C++20 support comes to mind, the plethora of supported hardware as well.

Re: C++20, How Hard Could It Be

#123

Post by pjmlp » Sun, Sep 25, 2022, 1:38 PM UTC

leni536 wrote: post #76

pjmlp wrote: post #47

Earlier quoted context omitted.

As if you could expect any kind of ABI compatibility between GCC and clang binary libraries today, and apparently it doesn't make them a complete garbage, go figure.

umm, you can edit: to elaborate both g++ and clang++ implement the Itanium C++ ABI[1]. You might get binary incompatibility by mixing standard libraries, so just don't do that. [1] https://itanium-cxx-abi.github.io/cxx-abi/abi.html

Which is exactly what happens when using shared objects.

Additionally the C++ ABI doesn't tell anything about how each binary library was compiled regarding compiler and linker switches that affect runtime behaviour.

Re: C++20, How Hard Could It Be

#124

Post by pjmlp » Sun, Sep 25, 2022, 1:40 PM UTC

JonChesterfield wrote: post #63

pjmlp wrote: post #14

Earlier quoted context omitted.

Thanks clang lagging behind ISO C++, you can use them today on Visual Studio 2022.

Clang had modules ages ago. Still does I think, but not the same thing as was standardised.

What it has are pseudo modules implementated via configuration files called module maps, completely unrelated to how C++20 modules work.

Re: C++20, How Hard Could It Be

#125

Post by pjmlp » Sun, Sep 25, 2022, 1:41 PM UTC

fouronnes3 wrote: post #88

misnome wrote: post #51

Wait, so the words "concepts" and "requires" were newly made keywords, and this breaks code, but the words "yield" and "await" were determined too important and too common to standards members that they needed to be renamed to the horrifically ugly "co_await" and "co_yield"? Also, last time I actually tried to use C++20 none of the standard library implementations had std::format; has this changed now?

One day in the far away future the standard C++ hello world will use 'import std;' and 'std::print' and it will be glorious.

Already available in C++23.

Re: C++20, How Hard Could It Be

#126

Post by philliphaydon » Sun, Sep 25, 2022, 1:43 PM UTC

This might be a stupid question. But is there performance degradation between versions of c++?

I saw a couple of stack overflow questions last week of people complaining about c++ 17 being slower 14, and 14 being slower than 11.

But I find it hard to believe. I just started learning c++ recently and can’t find a conclusive answer.

Re: C++20, How Hard Could It Be

#127

Post by pjmlp » Sun, Sep 25, 2022, 1:43 PM UTC

cletus wrote: post #116

Just a note but I'm fairly certain this is purely from the perspective of Google Chrome, meaning it excludes google3 (Google's repo for nearly all Google services). I don't know this for a fact but I suspect it's the case. I only bring it up because google3 C++ is (or was; it's now been years since I've done this directly) a very different beast. It was notionally compliant with recent standards but a very restrictiv…

The standard includes the standard library, a tiny set of pages when compared against Python, Java, F#, C# language reference, VM reference + standard library printout.

Re: C++20, How Hard Could It Be

#128

Post by arinlen » Sun, Sep 25, 2022, 1:46 PM UTC

cletus wrote: post #116

Just a note but I'm fairly certain this is purely from the perspective of Google Chrome, meaning it excludes google3 (Google's repo for nearly all Google services). I don't know this for a fact but I suspect it's the case. I only bring it up because google3 C++ is (or was; it's now been years since I've done this directly) a very different beast. It was notionally compliant with recent standards but a very restrictiv…

> The C++ standard currently sits at >1800 pages. Looking through these examples, I'm honestly horrified.

I feel you're embelishing too much your personal feeling of horror. The C++20 standard doc is a hair smaller than 1900 pages, but the complete core language is specified in the first 460 pages, of which around 100 are dedicated to templates.

Thus around 1400 pages of a 1900page doc are dedicated to specify libraries that throughout the years have been adopted by the standard. We're talking about stuff that was released with Boost and since then was deemed appropriate to make it standard.

Focusing on the 460 pages that specify the core language, most of this content has not been changed since C++98. The C++14 doc covered the core language with around 420 pages. Thus it makes zero sense to claim than suddenly C++ became horrifying because of the extra 20 sheets of paper you need to print out.

Re: C++20, How Hard Could It Be

#129

Post by scatters » Sun, Sep 25, 2022, 1:46 PM UTC

fouronnes3 wrote: post #88

misnome wrote: post #51

Wait, so the words "concepts" and "requires" were newly made keywords, and this breaks code, but the words "yield" and "await" were determined too important and too common to standards members that they needed to be renamed to the horrifically ugly "co_await" and "co_yield"? Also, last time I actually tried to use C++20 none of the standard library implementations had std::format; has this changed now?

One day in the far away future the standard C++ hello world will use 'import std;' and 'std::print' and it will be glorious.

The far away future? You mean next year?

Re: C++20, How Hard Could It Be

#130

Post by d110af5ccf » Sun, Sep 25, 2022, 1:46 PM UTC

philliphaydon wrote: post #126

This might be a stupid question. But is there performance degradation between versions of c++? I saw a couple of stack overflow questions last week of people complaining about c++ 17 being slower 14, and 14 being slower than 11. But I find it hard to believe. I just started learning c++ recently and can’t find a conclusive answer.

Those are just versions of the standard. What people would be comparing is the performance of particular implementations. It's entirely possible that a less mature implementation would have problems.