T& operator[](const key_type& x);
Effects:
Equivalent to: return try_emplace(x).first->second;
T& operator[](key_type&& x);
Effects:
Equivalent to: return try_emplace(move(x)).first->second;
T& at(const key_type& x);
const T& at(const key_type& x) const;
Returns:
A reference to the
mapped_type corresponding to
x in
*this. Throws:
An exception object of type
out_of_range if
no such element is present
.