c++ - Why does std::map not have a const accessor?

Question

The declaration for the [] operator on a std::map is this:

T& operator[] ( const key_type& x );

Is there a reason it isn't this?

T& operator[] ( const key_type& x );
const T& operator[] const ( const key_type& x );

Because that would be incredibly useful any time you need to access a member map in a const method.

Answer 1

As of C++11 there is std::map::at which offers const and non-const access.

In contrast to operator[] it will throw an std::out_of_range exception if the element is not in the map.