https://bugs.llvm.org/show_bug.cgi?id=40989
Bug ID: 40989
Summary: decltype resolution ignores SFINAE
Product: clang
Version: unspecified
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: C++11
Assignee: unassignedclangb...@nondot.org
Reporter: simon.rich...@hogyros.de
CC: blitzrak...@gmail.com, dgre...@apple.com,
erik.pilking...@gmail.com, llvm-bugs@lists.llvm.org,
richard-l...@metafoo.co.uk
GCC exhibits the same bug, see
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89564
This is related, but not identical to #40988.
I'm trying to build a commutative operator+ for a class, as a freestanding
template operator+ that accepts my class on the right hand side and reverses
the argument order:
#include <type_traits>
struct one {};
struct two
{
two() { }
two(one const &) { }
operator one() const { return one{}; }
};
template<typename T>
auto operator+(T const &lhs, two const &rhs) -> typename
std::enable_if<!std::is_same<T, two>::value, decltype(rhs + lhs)>::type
{
return rhs + lhs;
}
void test()
{
one o;
two t;
auto a = o + t;
}
This code should have been rejected, because no usable operator+ exists for the
expression "rhs + lhs". Instead, the template is specialized recursively trying
to resolve the decltype.
icc and MSVC correctly reject this code with the expected diagnostic.
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