std::experimental::ranges::EqualityComparable,(3) | C++ Standard Libary | std::experimental::ranges::EqualityComparable,(3) |

# NAME¶

std::experimental::ranges::EqualityComparable, - std::experimental::ranges::EqualityComparable,

# Synopsis¶

Defined in header <experimental/ranges/concepts>

template < class T >

concept bool EqualityComparable = WeaklyEqualityComparableWith<T,
**(1)** (ranges TS)

T>;

template <class T, class U>

concept bool EqualityComparableWith =

EqualityComparable<T> &&

EqualityComparable<U> &&

CommonReference<

const std::remove_reference_t<T>&, **(2)** (ranges TS)

const std::remove_reference_t<U>&> &&

EqualityComparable<

ranges::common_reference_t<

const std::remove_reference_t<T>&,

const std::remove_reference_t<U>&>> &&

WeaklyEqualityComparableWith<T, U>;

1) The concept EqualityComparable<T> specifies that the comparison
operators == and

!= on T reflects equality: == yields true if and only if the operands are
equal.

EqualityComparable<T> is satisfied only if, given objects a and b of
type T, bool(a

== b) is true if and only if a and b are equal. Together with the requirement
that a

== b is equality preserving, this implies that == is symmetric and
transitive, and

further that == is reflexive for all objects a that are equal to at least one
other

object.

2) The concept EqualityComparableWith<T, U> specifies that the
comparison operators

== and != on (possibly mixed) T and U operands yield results consistent with

equality. Comparing mixed operands yields results equivalent to comparing the

operands converted to their common type.

Formally, EqualityComparableWith<T, U> is satisfied only if, given any
lvalue t of

type const std::remove_reference_t<T> and any lvalue u of type const

std::remove_reference_t<U>, and let C be
ranges::common_reference_t<const

std::remove_reference_t<T>&, const
std::remove_reference_t<U>&>, bool(t == u) ==

bool(C(t) == C(u)).

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.

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.

2022.07.31 | http://cppreference.com |