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21st Century C++

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Re: 21st Century C++

#31

Post by skywal_l »

coffeeaddict1 wrote: post #18

The C++ Core Guidelines have existed for nearly 10 years now. Despite this, not a single implementation in any of the three major compilers exists that can enforce them. Profiles, which Bjarne et al have had years to work on, will not provide memory safety[0]. The C++ committee, including Bjarne Stroustrup, needs to accept that the language cannot be improved without breaking changes. However, it's already too late.…

I hoped Sean would open source Circle. It seemed promising, but it's been years and don't see any tangible progress. Maybe I am not looking hard enough?

Re: 21st Century C++

#32

Post by jcranmer »

senkora wrote: post #27
jjmarr wrote: post #6

Modules sound cool for compile time, but do they prevent duplicative template instantiations? Because that's the real performance killer in my experience.

The best way that I know of to do this is the """ "Manual" export templates """ idea discussed here: http://warp.povusers.org/programming/export_templates.html (It's a great post in general. N.B. that it's also quite old and export templates have been removed from the standard for quite some time after compiler writers refused to implement them.) TL;DR: Declare your templates in a header, implement them in a source f…

You can declare a template in a header file, and only provide its definition (and hence expansion) in a source file. See for example Firefox doing this for its string implementation here: https://searchfox.org/mozilla-central/source/xpcom/string/ns... (extern template declarations are at the end of the header file, and the actual template definitions are in https://searchfox.org/mozilla-central/source/xpcom/string/ns...).

Which is to say, "extern template" is a thing that exists, that works, and can be used to do what you want to do in many cases.

The "export template" feature was removed from the language because only one implementer (EDG) managed to implement them, and in the process discovered that a) this one feature was responsible for all of their schedule misses, b) the feature was far too annoying to actually implement, and c) when actually implemented, it didn't actually solve any of the problems. In short, when they were asked for advice on implementing export, all the engineers unanimously replied: "don't". (See https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n14... for more details).

Re: 21st Century C++

#33

Post by tialaramex »

hkwerf wrote: post #8
Night_Thastus wrote: post #4

Something about the formatting of the code blocks used is all messed up for me. Seems to be independent on browser, happens in both Firefox and Chrome.

It's typical Stroustrup style to write code in a variable width font. I'd wager they didn't have an option to use a variable-width font in their code blocks in their CMS and normal paragraphs are trimmed automatically. I didn't see the author at first. However, immediately after seeing the code I checked for the author, because I was sure it was Stroustrup.

The other give away is that he wants to use his awful "I/O streams" feature even though he also wants very modern features like modules.

Normal people who have a modern environment would std::println but Bjarne insists on using the I/O streams from last century instead

Re: 21st Century C++

#34

Post by janice1999 »

skywal_l wrote: post #31
coffeeaddict1 wrote: post #18

The C++ Core Guidelines have existed for nearly 10 years now. Despite this, not a single implementation in any of the three major compilers exists that can enforce them. Profiles, which Bjarne et al have had years to work on, will not provide memory safety[0]. The C++ committee, including Bjarne Stroustrup, needs to accept that the language cannot be improved without breaking changes. However, it's already too late.…

I hoped Sean would open source Circle. It seemed promising, but it's been years and don't see any tangible progress. Maybe I am not looking hard enough?

I think Carbon is more promising to be honest. They are aiming for something production-ready in 2027.

Re: 21st Century C++

#36

Post by tialaramex »

bluGill wrote: post #23
coffeeaddict1 wrote: post #18

The C++ Core Guidelines have existed for nearly 10 years now. Despite this, not a single implementation in any of the three major compilers exists that can enforce them. Profiles, which Bjarne et al have had years to work on, will not provide memory safety[0]. The C++ committee, including Bjarne Stroustrup, needs to accept that the language cannot be improved without breaking changes. However, it's already too late.…

Profiles will not provide perfect memory safety, but they go a long way to making things better. I have 10 million lines of C++. A breaking change (doesn't matter if you call it new C++ or Rust) would cost over a billion dollars - that is not happening. Which is to say I cannot use your perfect solution, I have to deal with what I have today and if profiles can make my code better without costing a full rewrite then…

Changes which re-define the language to have less UB will help you if you want safety/ correctness and are willing to do some work to bring that code to the newer language. An example would be the initialization rules in (draft) C++ 26. Historically C++ was OK with you just forgetting to initialize a primitive before using it, that's Undefined Behaviour in the language so... if that happens too bad all bets are off. In C++ 26 that will be Erroneous Behaviour and there's some value in the variable, it's not always guaranteed to be valid (which can be a problem for say, booleans or pointers) but just looking at the value is no longer UB and if you forgot to initialize say an int, or a char, that's fine since any possible bit sequence is valid, what you did was an error, but it's not necessarily fatal.

If you're not willing to do any work then you're just stuck, nobody can help you, magic "profiles" don't help either.

But, if you're willing to do work, why stop at profiles? Now we're talking about a price and I don't believe that somehow the minimum assignable budget is > $1Bn

Re: 21st Century C++

#37

Post by bluGill »

zozbot234 wrote: post #26
coffeeaddict1 wrote: post #18

The C++ Core Guidelines have existed for nearly 10 years now. Despite this, not a single implementation in any of the three major compilers exists that can enforce them. Profiles, which Bjarne et al have had years to work on, will not provide memory safety[0]. The C++ committee, including Bjarne Stroustrup, needs to accept that the language cannot be improved without breaking changes. However, it's already too late.…

> Profiles, which Bjarne et al have had years to work on, will not provide memory safety While I agree with this in a general sense, I think it ought to be quite possible to come up with a "profile" spec that's simply meant to enforce the language restriction/subsetting part of Safe C++ - meaning only the essentials of the safety checking mechanism, including the use of the borrow checker. Of course, this would not b…

I have seen 3 different safe c++ proposals (most are not papers yet, but they are serious efforts to show what safe c++ could look like). However there is a tradeoff here. the full bower checker in C++ approach is incompatible with all current C+++ and so adopting it is about as difficult is rewriting all your code in some other language. The other proposals are not as safe, but have different levels of you can use this with your existing code. All are not ready to get added to C++, but they all provide something better and I'm hopeful that something gets into C++ (though probably not before C++32)

Re: 21st Century C++

#38

Post by James_K »

npalli wrote: post #7
Night_Thastus wrote: post #4

Something about the formatting of the code blocks used is all messed up for me. Seems to be independent on browser, happens in both Firefox and Chrome.

This is a Bjarne issue. For personal reasons he uses proportional fonts in his code blocks (in his texts) instead of monospaced and the code snippets always look bad. I guess he is stuck in his ways, just have to work around this ugly look.

> This is a Bjarne issue.

I have come to find this category of error to be distressingly large.

Re: 21st Century C++

#39

Post by [deleted] »

bluGill wrote: post #23
coffeeaddict1 wrote: post #18

The C++ Core Guidelines have existed for nearly 10 years now. Despite this, not a single implementation in any of the three major compilers exists that can enforce them. Profiles, which Bjarne et al have had years to work on, will not provide memory safety[0]. The C++ committee, including Bjarne Stroustrup, needs to accept that the language cannot be improved without breaking changes. However, it's already too late.…

Profiles will not provide perfect memory safety, but they go a long way to making things better. I have 10 million lines of C++. A breaking change (doesn't matter if you call it new C++ or Rust) would cost over a billion dollars - that is not happening. Which is to say I cannot use your perfect solution, I have to deal with what I have today and if profiles can make my code better without costing a full rewrite then…

[deleted]

Re: 21st Century C++

#40

Post by bluGill »

tialaramex wrote: post #36
bluGill wrote: post #23

Earlier quoted context omitted.

Profiles will not provide perfect memory safety, but they go a long way to making things better. I have 10 million lines of C++. A breaking change (doesn't matter if you call it new C++ or Rust) would cost over a billion dollars - that is not happening. Which is to say I cannot use your perfect solution, I have to deal with what I have today and if profiles can make my code better without costing a full rewrite then…

Changes which re-define the language to have less UB will help you if you want safety/ correctness and are willing to do some work to bring that code to the newer language. An example would be the initialization rules in (draft) C++ 26. Historically C++ was OK with you just forgetting to initialize a primitive before using it, that's Undefined Behaviour in the language so... if that happens too bad all bets are off.…

The first part is why I'm excited for future C++ - they are making things better.

The reason I life profiles is they are not all or nothing. I can put them in new code only, or maybe a single file that I'm willing to take the time to refactor. Or at least so I hope, it remains to be seen if that is how they work out. I've been trying to figure out how to make rust fit in, but std::vector is a real pain to wrap into rust and so far I haven't managed to get anything done there.

The $1 billion is realistic - this project was a rewrite of a previous product that became unmaintainable and inflation adjusted the cost was $1 billion. You can maybe adjust that down a little if we are more productive, but not much. You can adjust it down a lot if you can come up with a way to keep our existing C++ and just extend new features and fix the old code only where it really is a problem. The code we have written in C++98 (because that was all we had in 2010) still compiles with the latest C++23 compiler and since there are no know bugs it isn't worth updating that code to the latest standards even though it would be a lot easier to maintain (which we never do) if we did.

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