Why should std::string's back() return a reference to a char?

Question

The std::string's back() returns a reference to a char. Why a ref?

      char& back();
const char& back() const;

Answer 1

A reference allows you to alter the value referred to. This follows the behaviour of other containers in the Standard Library.

Then the question becomes: why not return a reference?

Answer 2

Because the back() function on standard containers gives you a reference to the last element, so that you can do things with that element.

std::string provides you with the same interface.

Why shouldn't it?

Answer 3

Ok, I see the point for the non-const version where you may want to modify that char. Is there any benefit to & on the const version?

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It might be efficient, and it might not.