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C++ : if constexpr isn't broken

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Re: C++ : if constexpr isn't broken

#21

Post by seanmcdirmid »

adrianN wrote: post #13
moron4hire wrote: post #10

Earlier quoted context omitted.

I had a similar feeling. As a long-time C# programmer (how old is C#? That many years), I look at this and get really wide-eyed, "how is that at all a good idea?!" A lot of these features seem like ways to hack around the fact that C++ templates are not generics, they are literally templates for writing copies of classes. It seems like features like this are going to make code size explode. A lot of the examples also…

I'm not sure what you mean by generics if you think that C++ templates are not a kind of generics. Do you prefer that everything happens at runtime? Similarly, subclasses as opposed to templates carry a runtime cost. Virtual function calls are not free. Why pay that cost if you can deduce the right code from the types at compiletime? Besides, and this is probably a matter of opinion, I find code hard to follow that u…

C++ supports generic through template/macro expansion, rather than through parametric polymorphism.

Re: C++ : if constexpr isn't broken

#22

Post by maxxxxx »

jupp0r wrote: post #19
dasloop wrote: post #16

Earlier quoted context omitted.

Probably because you are used to the paralysed C++ pre C++11. Nothing happens for years and now we have new functionalities every three years supported by all major compilers. But, also, many new functionalities are not for global consumption. The audience of many meta programming functionalities are library developers for example.

Isn't every developer in a non-trivial software project a library developer? As soon as you have a common piece of functionality you want to reuse - that's a library.

I guess there are different levels of libraries. Something like boost is a different thing from encapsulating business logic into a library.

Re: C++ : if constexpr isn't broken

#23

Post by mattnewport »

Retra wrote: post #18
adrianN wrote: post #13

Earlier quoted context omitted.

I'm not sure what you mean by generics if you think that C++ templates are not a kind of generics. Do you prefer that everything happens at runtime? Similarly, subclasses as opposed to templates carry a runtime cost. Virtual function calls are not free. Why pay that cost if you can deduce the right code from the types at compiletime? Besides, and this is probably a matter of opinion, I find code hard to follow that u…

By "generics", I presume they mean template parameters which are checked at declaration, not at use.

That sounds like concepts, as used extensively in the OP.

Re: C++ : if constexpr isn't broken

#24

Post by [deleted] »

jupp0r wrote: post #19
dasloop wrote: post #16

Earlier quoted context omitted.

Probably because you are used to the paralysed C++ pre C++11. Nothing happens for years and now we have new functionalities every three years supported by all major compilers. But, also, many new functionalities are not for global consumption. The audience of many meta programming functionalities are library developers for example.

Isn't every developer in a non-trivial software project a library developer? As soon as you have a common piece of functionality you want to reuse - that's a library.

[deleted]

Re: C++ : if constexpr isn't broken

#25

Post by MichaelSalib »

jupp0r wrote: post #19
dasloop wrote: post #16

Earlier quoted context omitted.

Probably because you are used to the paralysed C++ pre C++11. Nothing happens for years and now we have new functionalities every three years supported by all major compilers. But, also, many new functionalities are not for global consumption. The audience of many meta programming functionalities are library developers for example.

Isn't every developer in a non-trivial software project a library developer? As soon as you have a common piece of functionality you want to reuse - that's a library.

I think that's dependent on language culture. Because the C++ community doesn't take language simplicity or comprehensibility seriously, there are lots of C++ developers who can't use or reason about surprisingly large parts of the language. So the community has rallied around the notion that "library" developers need to understand everything and that most developers will just glue together bits that the library devs made.

I mean, how many C++ developers actually write serious template code? How many of them could reliably explain what the keywords in post do?

The idea that every developer is a library author (or the lisp extension that every developer is a language author) is common in many other language communities but it relies on the community working hard to make mastery of the language feasible for lots of people. The C++ community never bought into that notion; they inherited a very stratified class structure from Bell Labs.

Re: C++ : if constexpr isn't broken

#26

Post by p0nce »

dasloop wrote: post #16
mark-r wrote: post #7

Why is it every time I see a new article about C++ features my eyes glaze over? Am I just getting old, or has C++ jumped the shark?

Probably because you are used to the paralysed C++ pre C++11. Nothing happens for years and now we have new functionalities every three years supported by all major compilers. But, also, many new functionalities are not for global consumption. The audience of many meta programming functionalities are library developers for example.

And that's exactly what's different in D, where the audience for meta-programming is "everyone". It's not just about more power, but how accessible this power is. To think you need to suffer to have this power is not true.

Re: C++ : if constexpr isn't broken

#27

Post by SamReidHughes »

neutronicus wrote: post #17
nivexous wrote: post #15

Earlier quoted context omitted.

In Bitcoin SV, there is a saying "devs gotta dev" to refer to the mass of crypto developers that add unnecessary complexity to their coins to solve minor or even nonexistant problems while not seeing the bigger (usually economic) picture. Everyone wants to make their mark on the space and there aren't enough leaders to direct the energy. C++ looks to be doing the same and not able to see the impact this will have on…

I disagree - I work in high-performance computing and I think in our case the complexity of C++ is actually mirroring that of the problem domain. Nothing else gives us the level of abstraction that C++ does, while still offering convenient ways to specify low-level performance semantics . I think for a while Fortran was pulling ahead for large-scale numerical computing, but the mess of different options for paralleli…

Looking at some C++ extension proposals, many are definitely a case of "devs gotta dev." Fortunately most of these don't have a chance in hell of making it in.

Re: C++ : if constexpr isn't broken

#28

Post by inetknght »

p0nce wrote: post #26
dasloop wrote: post #16

Earlier quoted context omitted.

Probably because you are used to the paralysed C++ pre C++11. Nothing happens for years and now we have new functionalities every three years supported by all major compilers. But, also, many new functionalities are not for global consumption. The audience of many meta programming functionalities are library developers for example.

And that's exactly what's different in D, where the audience for meta-programming is "everyone". It's not just about more power, but how accessible this power is. To think you need to suffer to have this power is not true.

Nothing stops "everyone" from using the features which suit library developers.

Re: C++ : if constexpr isn't broken

#29

Post by ska »

jupp0r wrote: post #19
dasloop wrote: post #16

Earlier quoted context omitted.

Probably because you are used to the paralysed C++ pre C++11. Nothing happens for years and now we have new functionalities every three years supported by all major compilers. But, also, many new functionalities are not for global consumption. The audience of many meta programming functionalities are library developers for example.

Isn't every developer in a non-trivial software project a library developer? As soon as you have a common piece of functionality you want to reuse - that's a library.

I understand this sentiment but think it is problematic. In fact, I think it is part of the reason a lot of libraries aren't very good.

Working in a large project, as you note, naturally leads to many conversations about sharing code and/or functionality. So you bundle something together or add an access point, call it "library X" and you are done, right? Any problems can be patched around later as you are working on a common base.

To me, this is missing > 50% of the work in designing and delivering a library for general use, which is why it often causes problems when you treat it as "done".

Which isn't to say this isn't the right thing to do in your situation! It's just that this is vastly different than what someone might be talking about in "library developer". It's not prima facie crazy to have language features mostly aimed at the latter, if it's a language often used for it. Which, for better or worse, c++ (still) is.

Re: C++ : if constexpr isn't broken

#30

Post by steveklabnik »

mattnewport wrote: post #23
Retra wrote: post #18

Earlier quoted context omitted.

By "generics", I presume they mean template parameters which are checked at declaration, not at use.

That sounds like concepts, as used extensively in the OP.

One significant difference with concepts is that they are optional.
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