[concept.boolean]

🔗

template<class B>
  concept Boolean =
    Movable<remove_cvref_t<B>> && // (see [concepts.object])
    requires(const remove_reference_t<B>& b1,
             const remove_reference_t<B>& b2, const bool a) {
      requires ConvertibleTo<const remove_reference_t<B>&, bool>;
      { !b1 } -> ConvertibleTo<bool>;
      { b1 &&  a } -> Same<bool>;
      { b1 ||  a } -> Same<bool>;
      { b1 && b2 } -> Same<bool>;
      {  a && b2 } -> Same<bool>;
      { b1 || b2 } -> Same<bool>;
      {  a || b2 } -> Same<bool>;
      { b1 == b2 } -> ConvertibleTo<bool>;
      { b1 ==  a } -> ConvertibleTo<bool>;
      {  a == b2 } -> ConvertibleTo<bool>;
      { b1 != b2 } -> ConvertibleTo<bool>;
      { b1 !=  a } -> ConvertibleTo<bool>;
      {  a != b2 } -> ConvertibleTo<bool>;
    };

Let b1 and b2 be lvalues of type const remove_reference_t<B>.

Boolean<B> is satisfied only if

(2.1)
bool(b1) == !bool(!b1).
(2.2)
(b1 && b2), (b1 && bool(b2)), and (bool(b1) && b2) are all equal to (bool(b1) && bool(b2)), and have the same short-circuit evaluation.
(2.3)
(b1 || b2), (b1 || bool(b2)), and (bool(b1) || b2) are all equal to (bool(b1) || bool(b2)), and have the same short-circuit evaluation.
(2.4)
bool(b1 == b2), bool(b1 == bool(b2)), and bool(bool(b1) == b2) are all equal to (bool(b1) == bool(b2)).
(2.5)
bool(b1 != b2), bool(b1 != bool(b2)), and bool(bool(b1) != b2) are all equal to (bool(b1) != bool(b2)).

[ Example

The types bool, true_type ([meta.type.synop]), and bitset<N>::reference ([template.bitset]) are Boolean types.

Pointers, smart pointers, and types with only explicit conversions to bool are not Boolean types.

— end example

]

17 Concepts library [concepts]

17.5 Comparison concepts [concepts.compare]

17.5.2 Concept Boolean [concept.boolean]