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c++gccclangtype-aliasname-mangling

Why do gcc and clang generate different symbol names for an instantiation of a function template?

Consider the following example:

struct A {
  using type = int;
};

template <typename T>
using B = A;

template <typename T>
typename B<T>::type f() { return {}; }

template B<int>::type f<int>();

Clang generates symbol named int f<int>() while GCC generates B::type f<int>() for the instantiation: https://godbolt.org/z/MCCza4

Why don't the compilers agree and shouldn't GCC also resolve B::type to int?

Solution

  • This is a known C++ CWG (Core Working Group) issue: https://wg21.cmeerw.net/cwg/issue2037, quoting Richard Smith:

    On the one hand, the alias template can introduce SFINAE conditions, so it should be instantiation-dependent and mangled. On the other hand, the language rules permit this template to be redeclared using the result of expanding the alias template, so mangling it can't be correct.