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std::equal_to

Defined in header `<functional>`
template< class T > struct equal_to;		(until C++14)
template< class T = void > struct equal_to;		(since C++14)

Function object for performing comparisons. Unless specialised, invokes operator== on type T.

Specializations

The standard library provides a specialization of std::equal_to when T is not specified, which leaves the parameter types and return type to be deduced.

equal_to<void>

(C++14)

function object implementing x == y deducing argument and return types
(class template specialization)

(since C++14)

Member types

Type	Definition
`result_type` (deprecated in C++17)(removed in C++20)	`bool`
`first_argument_type` (deprecated in C++17)(removed in C++20)	`T`
`second_argument_type` (deprecated in C++17)(removed in C++20)	`T`

These member types are obtained via publicly inheriting std::binary_function<T, T, bool>.

(until C++11)

Member functions

operator()

checks if the arguments are equal
(public member function)

std::equal_to::operator()

bool operator()( const T& lhs, const T& rhs ) const;		(until C++14)
constexpr bool operator()( const T& lhs, const T& rhs ) const;		(since C++14)

Checks whether lhs is equal to rhs.

Parameters

lhs, rhs

values to compare

Return value

true if lhs == rhs, false otherwise.

Exceptions

May throw implementation-defined exceptions.

Possible implementation

constexpr bool operator()(const T &lhs, const T &rhs) const 
{
    return lhs == rhs;
}

equal	determines if two sets of elements are the same (function template)
not_equal_to	function object implementing `x != y` (class template)
less	function object implementing `x < y` (class template)
ranges::equal_to (C++20)	function object implementing `x == y` (class)