Since gcc 3.4.0 I get an error message which is not very helpful for the
following invalid code snippet:

================================
struct A
{
    int operator[] (size_t);
};

struct B
{
    int foo(size_t);
};
================================

err.cc:3: error: declaration of `operator[]' as non-function
err.cc:3: error: expected `;' before '(' token
err.cc:8: error: expected `;' before '(' token

With gcc 3.3.5 and before I get:

err.cc:3: error: `size_t' was not declared in this scope
err.cc:3: error: invalid data member initialization
err.cc:3: error: (use `=' to initialize static data members)
err.cc:3: error: declaration of `operator[]' as non-function
err.cc:8: error: `size_t' was not declared in this scope
err.cc:8: error: invalid data member initialization

which says what's wrong: `size_t' was not declared in this scope.