24 Containers library [containers]

24.4 Associative containers [associative]

24.4.6 Class template set [set] Modifiers [set.modifiers]

template<class K> pair<iterator, bool> insert(K&& x); template<class K> iterator insert(const_iterator hint, K&& x);
Constraints: The qualified-id Compare​::​is_transparent is valid and denotes a type.
For the second overload, is_convertible_v<K&&, const_iterator> and is_convertible_v<K&&, iterator> are both false.
Preconditions: value_type is Cpp17EmplaceConstructible into set from std​::​forward<K>(x).
Effects: If the set already contains an element that is equivalent to x, there is no effect.
Otherwise, let r be equal_range(x).
Constructs an object u of type value_type with std​::​forward<K>(x).
If equal_range(u) == r is false, the behavior is undefined.
Inserts u into *this.
Returns: For 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 set element that is equivalent to x.
Complexity: Logarithmic.