Operator overload for [] operator

Question

Why would you need to overload the [] operator? I have never come across a practical scenario where this was necessary. Can somebody tell me a practical use case for this.

Answer 1

Err.. std::vector<t>, std::basic_string<t>, std::map<k, v>, and std::deque<t> ?

I used this for a class representing a registry key, where operator[] returned an object representing a registry value with the string between []s.

See also, the Spirit Parser Framework, which uses [] for semantic actions.