Comment by the_why_of_y

It depends... if your return type is nested inside a class and you're defining a member function, you'll have to write down a qualified return type name before the qualified member function name, whereas if the return type follows the function name, it can be unqualified because at that point the class extends the scope used for name lookup.

http://www.stroustrup.com/C++11FAQ.html#suffix-return