[map.cons]

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constexpr explicit map(const Compare& comp, const Allocator& = Allocator();

Effects: Constructs an empty map using the specified comparison object and allocator.

Complexity: Constant.

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template<class InputIterator>
  constexpr map(InputIterator first, InputIterator last,
                const Compare& comp = Compare(), const Allocator& = Allocator();

Effects: Constructs an empty map using the specified comparison object and allocator, and inserts elements from the range [first, last).

Complexity: Linear in N if the range [first, last) is already sorted with respect to comp and otherwise

N log N, where N is last - first .

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template<container-compatible-range<value_type> R>
  constexpr map(from_range_t, R&& rg, const Compare& comp = Compare(),
                const Allocator& = Allocator();

Effects: Constructs an empty map using the specified comparison object and allocator, and inserts elements from the range rg.

Complexity: Linear in N if rg is already sorted with respect to comp and otherwise

N log N, where N is ranges ​::​ distance (rg) .

23 Containers library [containers]

23.4 Associative containers [associative]

23.4.3 Class template map [map]

23.4.3.2 Constructors, copy, and assignment [map.cons]