https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71879
Bug ID: 71879
Summary: Error in unevaluated context breaks SFINAE
Product: gcc
Version: 6.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: manuel.schil...@bmw-carit.de
Target Milestone: ---
Having asked at Stackoverflow I was told the following might be a bug in GCC:
--------
When comparing member function pointers in an SFINAE context, member function
Foo::foo() exists, but its body contains code (x.hello()) which eventually does
not compile.
The following code compiles with clang. GCC however seems to evaluate the
function body of Foo::foo() and exits with an error ('struct Caller' has no
member named 'hello'), despite being in an unevaluated SFINAE context.
///
#include <iostream>
#include <type_traits>
struct Foo
{
template <typename T> void foo(T&& x) { x.hello();}
};
struct Caller
{
template <typename T>
auto call(T&& x, int) -> decltype(
std::enable_if_t<
std::is_same<
decltype(&T::template foo<decltype(*this)>),
void (T::*)(decltype(*this))
>::value
>())
{
//x.foo(*this);
}
template <typename T>
void call(T&&, char){ std::cout << "hello" << std::endl;}
};
int main()
{
Caller c;
c.call(Foo(), 0);
}
///
Error message:
main.cpp: In instantiation of 'void Foo::foo(T&&) [with T = Caller&]':
main.cpp:14:14: required by substitution of 'template<class T> decltype
(std::enable_if_t<std::is_same<decltype (& T:: foo<Caller&>), void
(T::*)(Caller&)>::value>()) Caller::call(T&&, int) [with T = Foo]'
main.cpp:31:18: required from here
main.cpp:6:47: error: 'struct Caller' has no member named 'hello'
template <typename T> void foo(T&& x) { x.hello(); }
~~^~~~~
------
version: g++ 6.1.0
flags: g++ -std=c++14 -O2 -Wall -pedantic -pthread main.cpp
------
Link to code on coliru: http://coliru.stacked-crooked.com/a/a984ad1ca2edcb0c
Link to stackoverflow: http://stackoverflow.com/q/38371924/678093
