boolean-testable
concept __boolean_testable_impl = std::convertible_to <B, bool>;
(exposition only*)
concept boolean-testable =
__boolean_testable_impl<B> &&
requires (B&& b) {
{ !std::forward <B>(b) } -> __boolean_testable_impl;
(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
types.
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).
[edit] Equality preservation
Expressions declared in requires expressions of the standard library concepts are required to be equality-preserving (except where stated otherwise).
[edit] Notes
Examples of boolean-testable
types include bool, std::true_type , std::bitset <N>::reference, and int*.
[edit] References
- C++23 standard (ISO/IEC 14882:2024):
- 18.5.2 Boolean testability [concept.booleantestable]
- C++20 standard (ISO/IEC 14882:2020):
- 18.5.2 Boolean testability [concept.booleantestable]