[Boost-users] About indirect_iterator

Hello, I want to use indirect_iterator and noticed that it subscript operator returns a proxy. I found the following explanation in iterator_facade.h: // A proxy return type for operator[], needed to deal with // iterators that may invalidate referents upon destruction. // Consider the temporary iterator in *(a + n) But I still don't understand why a proxy is necessary in some cases. Thank you in advance, Jens