https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68781
Bug ID: 68781
Summary: [concepts] requires in member function is not
unevaluated
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: jarrydb at cse dot unsw.edu.au
Target Milestone: ---
The following correct code fails to compile in r231384
template <typename T>
struct declval_helper
{
static constexpr bool stop = false;
static T value();
};
template <typename T>
T
declval()
{
static_assert(declval_helper<T>::stop, "declval must not be used");
return declval_helper<T>::value();
}
template <typename T>
struct A {
static void foo(int);
};
void bar(int);
template <typename T>
requires requires {
bar(declval<T>());
}
void foo(T t) {
}
class Foo {
public:
template <typename T>
requires requires {
bar(declval<T>());
}
void foo(T t) {
}
};
void test() {
Foo f;
f.foo(5);
foo(5);
}
with the error:
g++ -std=c++1z uneval.cpp -c
uneval.cpp: In instantiation of ‘T declval() [with T = int]’:
uneval.cpp:36:27: required by substitution of ‘template<class T> requires
predicate(requires{bar()((declval<T>)());}) void Foo::foo(T) [with T = int]’
uneval.cpp:45:12: required from here
uneval.cpp:12:5: error: static assertion failed: declval must not be used
static_assert(declval_helper<T>::stop, "declval must not be used");
^~~~~~~~~~~~~
Note that commenting out the line f.foo(5); works fine. So it is only a problem
for member functions.
