https://llvm.org/bugs/show_bug.cgi?id=23700
Bug ID: 23700
Summary: Superfluous instantiations during std::async overload
resolution
Product: libc++
Version: unspecified
Hardware: All
OS: All
Status: NEW
Severity: normal
Priority: P
Component: All Bugs
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected]
Classification: Unclassified
The following snippet triggers a compilation failure:
#include <future>
#include <type_traits>
struct foo {
template <class ...Ts>
void operator()(Ts...) {}
};
struct bar {
template <class T>
struct result {
static_assert(!std::is_integral<T>::value, "nope");
using type = T;
};
template <class T>
typename result<T>::type operator()(T v) { return v; }
};
int main() {
std::async(foo(), bar(), 42);
}
During overload resolution, the `async` overload taking a `launch` policy as
first argument is trying to instantiate `bar::operator()(int)` declaration,
resulting in an error that's not in the immediate context.
This snippet might be ill-formed given [temp.inst]/7
> If the overload resolution process can determine the correct function to call
> without instantiating a class template definition, it is unspecified whether
> that instantiation actually takes place.
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