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C++20 Concepts: The Definitive Guide

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Re: C++20 Concepts: The Definitive Guide

#21

Post by the_duke »

37ef_ced3 wrote: post #15
Koshkin wrote: post #12

Earlier quoted context omitted.

You can take K&R C from my cold, dead hands. There was no header file hell. Often you didn't need a single header to be included in your code: most functions returned int (or nothing), and if you needed something that returned double, you could just say so. I remember being excited about function prototypes, but something was irretrievably lost at that point. The primal elegance of C as it was conceived by its creato…

I think you're trying to say you like C but dislike C++'s complexity. You will enjoy Go. Go can be understood as an improved, modernized C that doesn't abandon C's simplicity.

The "Go is like C" comparison never made any sense to me.

Go has a sophisticated runtime with transparent N:M threading and built-in concurrency primitives, Interfaces, garbage collection and a large standard library.

Go is only simple when compared to the other languages that sit in a similar space, like Java and C#.

Re: C++20 Concepts: The Definitive Guide

#22

Post by lamp987 »

s-luv-j wrote: post #2

Is it just me, or have C++ errors gotten a lot better? Below example from guide seems a lot more ergonomic than in years past. test.cpp: In instantiation of ‘T add(T, T) [with T = std::basic_string ]’: test.cpp:17:21: required from here test.cpp:11:22: error: static assertion failed 11 | static_assert(std::is_integral_v ); | ~~~~~^~~~~~~~~~~~~~~~ test.cpp:11:22: note: ‘std::is_integral_v >’ evaluates to false Build f…

That has nothing to do with C++. Its entirely a compiler thing.

Re: C++20 Concepts: The Definitive Guide

#23

Post by agumonkey »

s-luv-j wrote: post #2

Is it just me, or have C++ errors gotten a lot better? Below example from guide seems a lot more ergonomic than in years past. test.cpp: In instantiation of ‘T add(T, T) [with T = std::basic_string ]’: test.cpp:17:21: required from here test.cpp:11:22: error: static assertion failed 11 | static_assert(std::is_integral_v ); | ~~~~~^~~~~~~~~~~~~~~~ test.cpp:11:22: note: ‘std::is_integral_v >’ evaluates to false Build f…

clang kinda started the race

Re: C++20 Concepts: The Definitive Guide

#24

Post by gmueckl »

eeegnu wrote: post #13

Something about type constraining auto just seems funny. I can see how it's useful from an error minimization / code clarity standpoint, but it almost seems counter to the point of even using auto.

I belive that you do not sufficiently understand the giant footgun that is unconstrained auto, especially in the context of very template-heavy code. Concepts solve the issue that judicious use of auto will allow template instantiations to succeed that are plain wrong in that they will happily do the wrong thing just because the types involved fit the constraints by mere chance and not because they were meant to be used together like this.

Re: C++20 Concepts: The Definitive Guide

#25

Post by in3d »

nrclark wrote: post #11

Another language-changing paradigm added to C++. I haven't even finished learning the old ones yet. Sometimes I think C++ would be better off if the committee stopped accepting proposals that add new features.

It’s true that C++ is huge but the complaint should be about the lack of epochs that would let us simplify the language instead of about very useful new features such as concepts, modules, or constexpr. If you’re already programming in C++ and you can’t take a few days every 3 years to learn about new additions, you’ll have even more problems with other languages.

Re: C++20 Concepts: The Definitive Guide

#26

Post by Someone »

bool3max wrote: post #18
Someone wrote: post #10

Earlier quoted context omitted.

One of clang’s stated goals is “expressive diagnostics” See https://clang.llvm.org/diagnostics.html ; that page is not dated, but compares to gcc 4.9, which is from April 22, 2014. gcc also has worked on improving its error messages (most likely because of competition with clang), so that comparison probably isn’t accurate anymore.

The link leads to a 404.

Thanks; HN thought the semicolon was part of the URL. Added a space.

Re: C++20 Concepts: The Definitive Guide

#27

Post by gpderetta »

eeegnu wrote: post #13

Something about type constraining auto just seems funny. I can see how it's useful from an error minimization / code clarity standpoint, but it almost seems counter to the point of even using auto.

Initially auto was not required (nor allowed). The concept name itself was enough. Adding auto is one of those compromises that please no one but was necessary to move the proposal forward

Re: C++20 Concepts: The Definitive Guide

#29

Post by pharmakom »

lamp987 wrote: post #22
s-luv-j wrote: post #2

Is it just me, or have C++ errors gotten a lot better? Below example from guide seems a lot more ergonomic than in years past. test.cpp: In instantiation of ‘T add(T, T) [with T = std::basic_string ]’: test.cpp:17:21: required from here test.cpp:11:22: error: static assertion failed 11 | static_assert(std::is_integral_v ); | ~~~~~^~~~~~~~~~~~~~~~ test.cpp:11:22: note: ‘std::is_integral_v >’ evaluates to false Build f…

That has nothing to do with C++. Its entirely a compiler thing.

True, although the distinction hardly matters to users.

Re: C++20 Concepts: The Definitive Guide

#30

Post by wk_end »

lamp987 wrote: post #22
s-luv-j wrote: post #2

Is it just me, or have C++ errors gotten a lot better? Below example from guide seems a lot more ergonomic than in years past. test.cpp: In instantiation of ‘T add(T, T) [with T = std::basic_string ]’: test.cpp:17:21: required from here test.cpp:11:22: error: static assertion failed 11 | static_assert(std::is_integral_v ); | ~~~~~^~~~~~~~~~~~~~~~ test.cpp:11:22: note: ‘std::is_integral_v >’ evaluates to false Build f…

That has nothing to do with C++. Its entirely a compiler thing.

Not entirely true - one of the motivations for new features and libraries C++ adds is to make better errors possible. In this case, `static_assert` was added in C++11, and `is_integral_v` was added in C++17. Concepts, the new feature this post is about, falls under that category as well.
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