Specifies that an expression of such a type and value category is convertible tobool, and for which the logical operators for the type or two differentBooleanTestable types have the usual behavior (includingshort-circuiting).

[edit]Requirements

Lete be an expression of a certain type and value category. The type and value category meet theBooleanTestable requirements if:

• !e is well-formed and does not modify the object denoted bye, if any, except that ife is an xvalue, the denoted object can be left in a valid but unspecified state(since C++11).
• Bothe and!e are convertible tobool by bothimplicit conversion andstatic_cast.
• Conversions in both manners produce equal results and do not modify the source object, if any, except that ife or!e is an xvalue, the source object can be left in a valid but unspecified state(since C++11).
• bool(!e)==!bool(e) holds.
• No viable non-memberoperator&& andoperator|| is visible byargument-dependent lookup for the type ofe or!e.
• Ife or!e is of a class type, the class does not define any memberoperator&& oroperator||.

[edit]Notes

The standard does not define a named requirement with this name. It was originally proposed in an early resolution ofLWG2114, but was superseded by the exposition-only conceptboolean-testable in the final resolutionP2167R3. Because implementations generally expect the provided types to modelboolean-testable even in pre-C++20 modes, we intentedly treat P2167R3 as a defect report and transform theboolean-testable to legacy named requirements.

When the&& and|| operators are used with operands whose type and value category areBooleanTestable, built-in versions are selected and short-circuit evaluation is performed.

Examples ofBooleanTestable types (with any value category) includebool,std::true_type(since C++11),std::bitset<N>::reference, andint*.

[edit]Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit]See also

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