The following testcase fails to compile: 

template <typename data1> struct outer1
{
    typedef int my_value_type;  // define a nested datatype

    template <typename servert> struct inner1
    {
        typedef outer1<data1> myboss;
// borrow the boss's datatype << -- don't reduce or change this one:
        typedef typename myboss::my_value_type my_value_type;
        my_value_type return_x();
    };

};

// g++ 4 choked on this one:
template <typename data1>
template <typename servert>
typename outer1<data1>::template inner1<servert>::my_value_type
outer1<data1>::inner1<servert>::return_x()
{
    return 4;
}

void testme()
{
    outer1<float>::inner1<int> Inner1;
    int rslt = Inner1.return_x(); // to instantiate and cause error
}


It is basically like this:
* outer1 class template has a nested datatype called "my_value_type"
* inner1 borrows the "my_value_type" from outer1 (its parent)

Then when we want to instantiate return_x() above, g++ gives the following error:

template-typename4.cpp:19: error: prototype for ‘typename outer1<data1>::inner1<servert>::my_value_type outer1<data1>::inner1<servert>::return_x()’ does not match any in class ‘outer1<data1>::inner1<servert>’
template-typename4.cpp:10: error: candidate is: typename outer1<data1>::my_value_type outer1<data1>::inner1<servert>::return_x()
template-typename4.cpp:19: error: template definition of non-template ‘typename outer1<data1>::inner1<servert>::my_value_type outer1<data1>::inner1<servert>::return_x()’

I can work around this by changing line 18 above:

  typename outer1<data1>::template inner1<servert>::my_value_type

to

  typename outer1<data1>::my_value_type

then it would compile. But I think this is a bug. It used to compile with g++ 3. Other compilers such as Intel C++ (version 9.1), PGI C++ 7 all accept this language construct.