Difference between revisions of "cpp/concepts/boolean-testable"
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{{dcl|since=c++20|1= | {{dcl|since=c++20|1= | ||
template<class B> | template<class B> | ||
| − | concept boolean-testable = | + | concept boolean-testable = // exposition only |
__boolean_testable_impl<B> && | __boolean_testable_impl<B> && | ||
requires (B&& b) { | requires (B&& b) { | ||
Revision as of 20:49, 12 July 2020
| template<class B> concept __boolean_testable_impl = // exposition only |
(since C++20) | |
| template<class B> concept boolean-testable = // exposition only |
(since C++20) | |
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).
Equality preservation
Expressions declared in requires expressions of the standard library concepts are required to be equality-preserving (except where stated otherwise).
Notes
Examples of boolean-testable types include bool, std::true_type, and std::bitset<N>::reference, and int*.
