std::ranges::equal_to
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ranges::equal_to
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Defined in header
<functional>
struct equal_to;
(since C++20)
Function object for performing comparisons. The parameter types of the function call operator (but not the return type) are deduced from the arguments.
Contents
[edit] Nested types
Nested type
Definition
is_transparent
unspecified
[edit] Member functions
operator()
(public member function)
std::ranges::equal_to::operator()
template< class T, class U >
constexpr bool operator()( T&& t, U&& u ) const;
constexpr bool operator()( T&& t, U&& u ) const;
Given the expression std::forward <T>(t) == std::forward <U>(u) as expr:
- If expr results in a call to built-in operator== comparing pointers, given the composite pointer type of t and u as
P:
- For the two converted pointers (of type
P), if one pointer precedes the other in the implementation-defined strict total order over pointers, returns false, otherwise returns true. - If the conversion sequence from
TtoPor the conversion sequence fromUtoPis not equality-preserving, the behavior is undefined.
- For the two converted pointers (of type
- Otherwise:
- Returns the result of expr.
- If std::equality_comparable_with <T, U> is not modeled, the behavior is undefined.
This overload participates in overload resolution only if std::equality_comparable_with <T, U> is satisfied.
[edit] Notes
Compared to std::equal_to , std::ranges::equal_to additionally requires != to be valid, and that both argument types are required to be (homogeneously) comparable with themselves (via the equality_comparable_with constraint).
[edit] Example
This section is incomplete
Reason: no example
Reason: no example
[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 3530 | C++20 | syntactic checks were relaxed while comparing pointers | only semantic requirements are relaxed |