Invalid code in 11.Templates_II Other Notes

[alarxx]

In first example you can't do that for a function, but you can for a class:

template <int ... IntSeq>
class A {}; // Ok

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For functions you can use variadic templates with SFINAE type check or with requires (C++20) or as it is written below with auto, it seems to be called "abbreviated function templates", but specifically as it is written here, it doesn't work that way.

I believe this solution should work below С++20:

#include <type_traits>
template <typename ... TArgs, typename = std::enable_if_t<(std::conjunction_v<std::is_same<TArgs, int>...>)>> // SFINAE
void fun(const TArgs ... args) {}

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The first example from slide will generate an error:

template <int ... IntSeq>
void f(IntSeq ... seq){} // Error

int main(){}

g++ main.cpp -Wall -std=c++23 && ./a.out

Output:

main.cpp:2:6: error: variable or field ‘f’ declared void
    2 | void f(IntSeq ... seq){}
      |      ^
main.cpp:2:18: error: expected ‘)’ before ‘seq’
    2 | void f(IntSeq ... seq){}
      |       ~          ^~~~
      |                  )