The following code is very short, but causes different compilers to behave disagree:
#include <tuple> template <typename T = int, typename... Ts> using tpl = std::tuple<T, Ts...>; tpl x; // I would assume this should be std::tuple<int>
Clang and MSVC say that template argument deduction doesn’t work for alias templates, ICC says that template arguments are missing, while GCC has an
internal compiler error. I would normaly consider that an indication that alias templates do not undergo deduction – especially that according to cppreference they don’t (which I am aware is not an official resource and just a reference) – but I would like to be sure.
Is this code really ill-formed or are alias template default template arguments simply not yet implemented in these compilers? I thought that they were added in C++17 or C++20.
Source: Windows Questions C++