Difference between revisions of "cpp/concepts/boolean-testable"
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{{cpp/concepts/navbar}} | {{cpp/concepts/navbar}} | ||
{{dcl begin}} | {{dcl begin}} | ||
| − | {{ | + | {{dcla|anchor=no|num=1|since=c++20|expos=yes|1= |
| − | template<class B> | + | template< class B > |
| − | concept __boolean_testable_impl = | + | concept __boolean_testable_impl = std::convertible_to<B, bool>; |
| − | + | ||
}} | }} | ||
| − | {{ | + | {{dcla|anchor=no|num=2|since=c++20|expos=yes|1= |
| − | template<class B> | + | template< class B > |
| − | concept boolean-testable = | + | concept boolean-testable = |
__boolean_testable_impl<B> && | __boolean_testable_impl<B> && | ||
requires (B&& b) { | requires (B&& b) { | ||
| − | { !std::forward<B>(b) } -> __boolean_testable_impl | + | { !std::forward<B>(b) } -> __boolean_testable_impl; |
}; | }; | ||
}} | }} | ||
{{dcl end}} | {{dcl end}} | ||
| − | The exposition-only concept {{ | + | The exposition-only concept {{tti|boolean-testable}} specifies the requirements for expressions that are convertible to {{c/core|bool}} and for which the logical operators have the usual behavior (including {{enwiki|Short-circuit evaluation|short-circuiting}}), even for two different {{tti|boolean-testable}} types. |
| − | Formally, to model the exposition-only concept {{ | + | Formally, to model the exposition-only concept {{tti|__boolean_testable_impl}}, the type must not define any member {{c/core|operator&&}} and {{c/core|operator{{!!}}}}, and no viable non-member {{c/core|operator&&}} and {{c/core|operator{{!!}}}} may be visible by [[cpp/language/adl|argument-dependent lookup]]. Additionally, given an expression {{tt|e}} such that {{c|decltype((e))}} is {{tt|B}}, {{tti|boolean-testable}} is modeled only if {{c|1=bool(e) == !bool(!e)}}. |
{{cpp/concepts/equality preservation}} | {{cpp/concepts/equality preservation}} | ||
| − | === Notes=== | + | ===Notes=== |
| − | Examples of {{ | + | Examples of {{tti|boolean-testable}} types include {{c/core|bool}}, {{lc|std::true_type}}, {{c/core|std::bitset<N>::}}{{ltt|cpp/utility/bitset/reference}}, and {{c/core|int*}}. |
| + | |||
| + | ===References=== | ||
| + | {{ref std c++23}} | ||
| + | {{ref std|section=18.5.2|title=Boolean testability|id=concept.booleantestable}} | ||
| + | {{ref std end}} | ||
| + | {{ref std c++20}} | ||
| + | {{ref std|section=18.5.2|title=Boolean testability|id=concept.booleantestable}} | ||
| + | {{ref std end}} | ||
{{langlinks|es|ja|zh}} | {{langlinks|es|ja|zh}} | ||
Latest revision as of 05:15, 9 September 2024
template< class B > concept __boolean_testable_impl = std::convertible_to<B, bool>; |
(1) | (since C++20) (exposition only*) |
template< class B > concept boolean-testable = |
(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 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]
