Prior to commit 2aa1056, the Destructible concept was defined in terms of std::is_destructible. Following that commit, it is defined using a requires expression that uses an explicit destructor call and requires that a pointer to the type can be constructed.
The current Destructible concept fails for some types that are destructible according to the libstdc++ std::is_destructible implementation; specifically for reference types and arrays of known bound. The following example demonstrates this:
$ cat destructible.cpp
#include <type_traits>
template<typename T>
concept bool
Destructible()
{
#if USE_IS_DESTRUCTIBLE
return std::is_destructible<T>::value;
#else
return requires (T* t) { t->~T(); };
#endif
}
template<Destructible T>
void f();
void bar() {
f<char[5]>(); // constraints not satisfied; ok with is_destructible
f<int&>(); // constraints not satisfied; ok with is_destructible
}$ g++ -c -std=c++1z -DUSE_IS_DESTRUCTIBLE destructible.cpp
$ g++ -c -std=c++1z destructible.cpp
destructible.cpp: In function ‘void bar()’:
destructible.cpp:18:16: error: cannot call function ‘void f() [with T = char [5]]’
f<char[5]>(); // constraints not satisfied; ok with is_destructible
^
destructible.cpp:15:6: note: constraints not satisfied
void f();
^
destructible.cpp:15:6: note: concept ‘Destructible<char [5]>()’ was not satisfied
destructible.cpp:19:13: error: cannot call function ‘void f() [with T = int&]’
f<int&>(); // constraints not satisfied; ok with is_destructible
^
destructible.cpp:15:6: note: constraints not satisfied
void f();
^
destructible.cpp:15:6: note: concept ‘Destructible<int&>()’ was not satisfied
I don't know what motivated the change to the Destructible concept definition. Unless there is good reason to avoid std::is_destructible, I recommend reverting the change to the concept definition.
Relevant C++ DRs:
Prior to commit 2aa1056, the Destructible concept was defined in terms of std::is_destructible. Following that commit, it is defined using a requires expression that uses an explicit destructor call and requires that a pointer to the type can be constructed.
The current Destructible concept fails for some types that are destructible according to the libstdc++ std::is_destructible implementation; specifically for reference types and arrays of known bound. The following example demonstrates this:
$ cat destructible.cpp
$ g++ -c -std=c++1z -DUSE_IS_DESTRUCTIBLE destructible.cpp
$ g++ -c -std=c++1z destructible.cpp
I don't know what motivated the change to the Destructible concept definition. Unless there is good reason to avoid std::is_destructible, I recommend reverting the change to the concept definition.
Relevant C++ DRs: