24 Containers library [containers]

24.5 Unordered associative containers [unord]

24.5.4 Class template unordered_map [unord.map]

24.5.4.4 Modifiers [unord.map.modifiers]

template<class P>
  pair<iterator, bool> insert(P&& obj);

Constraints: is_constructible_v<value_type, P&&> is true.

Effects: Equivalent to: return emplace(std::forward<P>(obj));

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template<class P>
  iterator insert(const_iterator hint, P&& obj);

Constraints: is_constructible_v<value_type, P&&> is true.

Effects: Equivalent to: return emplace_hint(hint, std::forward<P>(obj));

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template<class... Args>
  pair<iterator, bool> try_emplace(const key_type& k, Args&&... args);
template<class... Args>
  iterator try_emplace(const_iterator hint, const key_type& k, Args&&... args);

Preconditions: value_type is Cpp17EmplaceConstructible into unordered_map from piecewise_construct, forward_as_tuple(k), forward_as_tuple(std::forward<Args>(args)...).

Effects: If the map already contains an element whose key is equivalent to k, there is no effect.

Otherwise inserts an object of type value_type constructed with piecewise_construct, forward_as_tuple(k), forward_as_tuple(std::forward<Args>(args)...).

Returns: In the first overload, the bool component of the returned pair is true if and only if the insertion took place.

The returned iterator points to the map element whose key is equivalent to k.

Complexity: The same as emplace and emplace_hint, respectively.

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template<class... Args>
  pair<iterator, bool> try_emplace(key_type&& k, Args&&... args);
template<class... Args>
  iterator try_emplace(const_iterator hint, key_type&& k, Args&&... args);

Preconditions: value_type is Cpp17EmplaceConstructible into unordered_map from piecewise_construct, forward_as_tuple(std::move(k)), forward_as_tuple(std::forward<Args>(args)...).

Effects: If the map already contains an element whose key is equivalent to k, there is no effect.

Otherwise inserts an object of type value_type constructed with piecewise_construct, forward_as_tuple(std::move(k)), forward_as_tuple(std::forward<Args>(args)...).

Returns: In the first overload, the bool component of the returned pair is true if and only if the insertion took place.

The returned iterator points to the map element whose key is equivalent to k.

Complexity: The same as emplace and emplace_hint, respectively.

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template<class M>
  pair<iterator, bool> insert_or_assign(const key_type& k, M&& obj);
template<class M>
  iterator insert_or_assign(const_iterator hint, const key_type& k, M&& obj);

Mandates: is_assignable_v<mapped_type&, M&&> is true.

Preconditions: value_type is Cpp17EmplaceConstructible into unordered_map from k, std::forward<M>(obj).

Effects: If the map already contains an element e whose key is equivalent to k, assigns std::forward<M>(obj) to e.second.

Otherwise inserts an object of type value_type constructed with k, std::forward<M>(obj).

Returns: In the first overload, the bool component of the returned pair is true if and only if the insertion took place.

The returned iterator points to the map element whose key is equivalent to k.

Complexity: The same as emplace and emplace_hint, respectively.

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template<class M>
  pair<iterator, bool> insert_or_assign(key_type&& k, M&& obj);
template<class M>
  iterator insert_or_assign(const_iterator hint, key_type&& k, M&& obj);

Mandates: is_assignable_v<mapped_type&, M&&> is true.

Preconditions: value_type is Cpp17EmplaceConstructible into unordered_map from std::move(k), std::forward<M>(obj).

Effects: If the map already contains an element e whose key is equivalent to k, assigns std::forward<M>(obj) to e.second.

Otherwise inserts an object of type value_type constructed with std::move(k), std::forward<M>(obj).

Returns: In the first overload, the bool component of the returned pair is true if and only if the insertion took place.

The returned iterator points to the map element whose key is equivalent to k.

Complexity: The same as emplace and emplace_hint, respectively.