Same function with const and without - When and why?

Question

T& f() { // some code ... }
const T& f() const { // some code ... }

I\'ve seen this a couple of times now (in the introductory book I\'ve b

Answer 1

As it was mentioned before, you can use const and non-const versions of functions depending on the const-ness of the invoking object. The paradigm is very often used with operator[] for arrays. A way to avoid code duplication (taken from Scott Meyers' book Effective C++) is to const_cast the const function return in a non-const overload, such as:

// returns the position of some internal char array in a class Foo
const char& Foo::operator[](std::size_t position) const
{
    return arr[position]; // getter 
}

// we now define the non-const in terms of the const version
char& Foo::operator[](std::size_t position) 
{
    return const_cast( // cast back to non-const
        static_cast(*this)[position] // calls const overload
    ); // getter/setter
}