NAME

std::experimental::ranges::Boolean - std::experimental::ranges::Boolean

Synopsis

Defined in header <experimental/ranges/concepts>
template <class B>

concept bool Boolean =
Movable<std::decay_t<B>> &&
requires(const std::remove_reference_t<B>& b1,
const std::remove_reference_t<B>& b2, const bool a) {
{ b1 } -> ConvertibleTo<bool>&&;
{ !b1 } -> ConvertibleTo<bool>&&;
{ b1 && a } -> Same<bool>&&;
{ b1 || a } -> Same<bool>&&;
{ b1 && b2 } -> Same<bool>&&; (ranges TS)
{ 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>&&;

};

The concept Boolean<B> specifies the requirements for a type usable in Boolean
contexts. For Boolean to be satisfied, the logical operators must have the usual
behavior (including short-circuiting). More precisely, given

* b1, b2, two lvalues of type const std::remove_reference_t<B>,

Boolean<B> is satisfied only if:

* bool(b1) == !bool(!b1)
* b1 && b2, b1 && bool(b2) and bool(b1) && b2 are all equal to bool(b1) &&
bool(b2) and have the same short-circuit evaluation;
* b1 || b2, b1 || bool(b2) and bool(b1) || b2 are all equal to bool(b1) ||
bool(b2) and have the same short-circuit evaluation;
* bool(b1 == b2), bool(b1 == bool(b2)), and bool(bool(b1) == b2) are all equal to
(bool(b1) == bool(b2));
* bool(b1 != b2), bool(b1 != bool(b2)), and bool(bool(b1) != b2) are all equal to
(bool(b1) != bool(b2)).

Equality preservation

An expression is equality preserving if it results in equal outputs given equal
inputs.

* The inputs to an expression consist of its operands.
* The outputs of an expression consist of its result and all operands modified by
the expression (if any).

Every expression required to be equality preserving is further required to be
stable: two evaluations of such an expression with the same input objects must have
equal outputs absent any explicit intervening modification of those input objects.

Unless noted otherwise, every expression used in a requires-expression is required
to be equality preserving and stable, and the evaluation of the expression may only
modify its non-constant operands. Operands that are constant must not be modified.

Implicit expression variations

A requires-expression that uses an expression that is non-modifying for some
constant lvalue operand also implicitly requires additional variations of that
expression that accept a non-constant lvalue or (possibly constant) rvalue for the
given operand unless such an expression variation is explicitly required with
differing semantics. These implicit expression variations must meet the same
semantic requirements of the declared expression. The extent to which an
implementation validates the syntax of the variations is unspecified.

Notes

Examples of Boolean types include bool, std::true_type, and
std::bitset<N>::reference. Pointers are not Boolean types.

A deduction constraint of the form { expression } -> Same<T>&& effectively requires
decltype((expression))&& to be the exact same type as T&&. This constrains both the
expression's type and its value category.