Does this detection idiom correctly report whether `T` has a member `.size()`? What does `has_size<std::string>::value` yield?

#include <type_traits> template <typename T, typename = void> struct has_size : std::false_type {}; template <typename T> struct has_size<T, std::void_t<decltype(std::declval<T>().size())>> : std::true_type {};