CppCon 2018: Walter E. Brown “C++ Function Templates: How Do They Really Work?”
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- čas přidán 3. 06. 2024
- CppCon.org
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Presentation Slides, PDFs, Source Code and other presenter materials are available at: github.com/CppCon/CppCon2018
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This talk will focus on C++ function templates and such allied topics as compiler-synthesized function template declarations/signatures, overload resolution and partial ordering of these declarations, and compiler instantiation of function template definitions.
We’ll also look at function template specialization, explaining why to avoid explicit ones, and recommending what to do instead.
Finally, time permitting, we’ll offer advice for customizing function templates in the standard library, especially in light of recent WG21 developments re customization points.
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Walter E. Brown
retired
With broad experience in industry, academia, consulting, and research, Dr. Walter E. Brown has been a C++ programmer for over thirty-five years, joining the C++ standards effort in 2000. Among numerous other contributions, he is responsible for introducing such now-standard C++ library features as cbegin/cend, common_type, gcd, and void_t, as well as headers ＜random＞ and ＜ratio＞. He has also significantly impacted such core language features as alias templates, contextual conversions, variable templates, and static_assert. He conceived and served as project editor for the International Standard on Mathematical Special Functions in C++, now part of C++17.When not playing with his grandchildren, Dr. Brown is an Emeritus participant in the C++ standards process, with several more core and library proposals under consideration.
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Videos Filmed & Edited by Bash Films: www.BashFilms.com
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When I previewed this and saw it was slides with lots of text, I thought "Oh, no, another talk where someone is just going to read slides to us", and expected to move on to something else after about 5 minutes. I'm glad I didn't. If you watch nothing else, watch the sections that cover slides 20 through 22. I've been using C++ since the mid 90s, and I've never seen what he talks about there presented better than he does.
Very clear and informative talk. Thank you.
Coffee, fruit cake, and a walter brown video.
You saved my day trying to understand Explicit Specialisation. Much respect to you!!!
As usual, yet another very clear presentation from Walter
An excellent talk! I learned so much from this. Thanks Walter!
49:30 - 51:30 The abbreviated function templates and the constraints - including the adjective syntax - are in C++20. ❤
44:22 I’m not saying everything about C++ is perfectly named, but STL stands for _standard template library,_ so no surprise there’s a lot of templates in it.
Excellent talk. One question from me, could anyone explain what "name" refer to in "Specialization of a template does not introduce a name"?
slide 22:
Is it possible to create specialization (b) of (a) after the declaration of (c) or will it always become specialization (d) ?
Someone asks this question at the end. I'd say try it.
Yes: godbolt.org/z/5hrhh8
After
template void f(T) { .. } // A
template void f(T*) { .. } // B
you can specialize both by explicitly providing template arguments. If you want an explicit specialization that takes int*:
template void f(int*) { .. } // special A, explicit type arg required
template void f(int*) { .. } // special B, version with explicit type arg
template void f(int*) { .. } // spacial B, version without explicit type arg
I want to have,
T someFunction (T t) { }
become
std::string someFunction(std::string t) { }
when called with a string literal like
someFunction("somestring")
How would I do that? Type traits? Overloaded proxy w/ explicit cast? What's the idiomatic way?
48:50 It does not seem like std::swap finds another swap in C++20/23, but std::range::swap does. So, use the latter or do the 2-step dance.
-- "Function templates are special functions ..."
Conceptually, they can be seen as functions (in a mathematical sense) that take types as arguments and spit out a function (in a C++ sense).
Exactly, templates are like mathematical mappings (functions), which take arguments and map to functions.
Exaxtly, they are functions input types output plain c++ functions, computed by compiler.
Exactly #3, I'm surprised that none called him on that. Templates clearly map some things to some other things. His implied argument against it is that we can't call them, yet we can definitely observe them :). To give him the benefit of a doubt, he might have wanted to mean that thinking of them as "functions" is unhelpful. But to state that they are notany kind of function is blatantly wrong. Furthermore, without having the context of the quotes he presented we can't be sure whether they were used wrong or not.
and this is the problem with academic types - function template does not have to be visible in "its entirety" , that is why in c++ we have linker , forward declaration /specialization is perfectly acceptable in c++ ( it is not java , the gentleman is probably confused about that )
Why the hell do i need to invest space in my brain to hold those rules? Just dont write code in such a way. A code should be cleanly understandable with minimal amount of knowledge and mental work. Inserting artificial rules to solve artificial problems, and expecting people to remember those rules is innefficient.
I feel bad for all those compiler developers that have to put up with all these non senses
No no… ;
This because our Mathematical level goes down and down;
And other thing that all compiler designers were Mathematicians first before CS; and As Mathematician I like and i work to put thing more general and universal of use and make C++ very close and close to maths Axiomatic.