I need to pass pointers to member functions as parameters to other functions. I use std::mem_fn
to wrap those in function objects.
Sometimes the member functions have overloads. I learned two syntax forms to disambiguate the overloads:
T::template member<template-args>
in the pointer-to-member expression.mem_fn
: mem_fn<return-type(args-types)>(pointer-to-member-expression)
.But what syntax should be used to disambiguate a non-template member function when some overloads are template member functions? My straightforward guess does not compile:
#include <iostream> // cout
#include <functional> // mem_fn
struct C {
void f() { std::cout << "f()\n"; }
void f(int) { std::cout << "f(int)\n"; }
template <class T>
void g(T) { std::cout << "g(T)\n"; }
template <class T1, class T2>
void g(T1) { std::cout << "g<T1,T2>(T1)\n"; }
template <class T>
void h(T) { std::cout << "h(T)\n"; }
void h(int) { std::cout << "h(int)\n"; }
};
int main() {
C c;
// non-template member function vs non-template member function
std::mem_fn<void()>(&C::f)(c);
std::mem_fn<void(int)>(&C::f)(c, 1);
// template member function vs template member function
std::mem_fn(&C::template g<int>)(c, 1);
std::mem_fn(&C::template g<int, int>)(c, 1);
// non-template member function vs template member function
std::mem_fn(&C::template h<int>)(c, 1);
// gcc: error: no matching function for call to 'mem_fn<void(int)>(<unresolved overloaded function type>)'
// clang: error: no matching function for call to 'mem_fn'
// std::mem_fn<void(int)>(&C::h)(c, 1);
return 0;
}
See also: https://godbolt.org/z/39dd569cK
FWIW I use C++20 but see the same errors also in C++11.