include/require inside of function

Is there anyway to include a file inside of a function and have the included stuff be global? For instance if I defined a class or a function in that include file, I want to be able to use that class outside of the function. On the documentation for include() a poster commented that it did indeed work like this, but my testing indicates it does not. Everything stays local to the function and goes away when the function ends. Is there a way?