# std::pmr::operator==, std::pmr::operator!=

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< cpp‎ | memory‎ | polymorphic allocator

Defined in header `<memory_resource>` |  |
template< class T1, class T2 > bool operator==( const std::pmr::polymorphic_allocator<T1>& lhs, const std::pmr::polymorphic_allocator<T2>& rhs ) noexcept; | (1) | (since C++17)
friend bool operator==( const polymorphic_allocator& lhs, const polymorphic_allocator& rhs ) noexcept; | (2) | (since C++17)
template< class T1, class T2 > bool operator!=( const std::pmr::polymorphic_allocator<T1>& lhs, const std::pmr::polymorphic_allocator<T2>& rhs ) noexcept; | (3) | (since C++17) (until C++20)
friend bool operator!=( const polymorphic_allocator& lhs, const polymorphic_allocator& rhs ) noexcept; | (4) | (since C++17) (until C++20)

Compares two polymorphic allocators. Two polymorphic allocators compare equal if their underlying memory resource compares equal.

1) Returns *lhs.resource() == *rhs.resource().
2) Same as (1), allowing conversion to `polymorphic_allocator`.
This function is not visible to ordinary unqualified or qualified lookup, and can only be found by argument-dependent lookup when `std::pmr::polymorphic_allocator` is an associated class of the arguments.
3) Returns !(lhs == rhs).
4) Same as (3), allowing conversion to `polymorphic_allocator`.
This function is not visible to ordinary unqualified or qualified lookup, and can only be found by argument-dependent lookup when `std::pmr::polymorphic_allocator` is an associated class of the arguments.

The `!=` operator is synthesized from `operator==`. | (since C++20)

### Parameters

lhs, rhs | - | polymorphic allocators to compare

### Return value

1-2) *lhs.resource() == *rhs.resource()
3-4) !(lhs == rhs)

### 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 3683 | C++17 | `polymorphic_allocator` could not be compared with types convertible to it | overload added

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