boolean-testable

template < class B > concept __boolean_testable_impl = std::convertible_to <B, bool > ;	(1)	(since C++20) (exposition only*)
template < class B > concept boolean-testable =     __boolean_testable_impl<B> &&     requires (B&& b) { { ! std::forward <B> (b) } - > __boolean_testable_impl; } ;	(2)	(since C++20) (exposition only*)

The exposition-only concept boolean-testable specifies the requirements for expressions that are convertible to bool and for which the logical operators have the usual behavior (including short-circuiting), even for two different boolean-testable

Formally, to model the exposition-only concept __boolean_testable_impl, the type must not define any member operator&& and operator||, and no viable non-member operator&& and operator|| may be visible by argument-dependent lookup. Additionally, given an expression e such that decltype((e)) is B, boolean-testable is modeled only if bool (e) == ! bool ( !e)

Equality preservation

Expressions declared in requires expressions of the standard library concepts are required to be equality-preserving

Notes

Examples of boolean-testable types include bool, std::true_type, std::bitset<N>:: reference, and int*

References