.stringof might call function?

[simendsjo]

Why is the function called in the template at the line of 
.stringof?

template t(alias fn) {
    static if(fn.stringof) // f(int i) isn't callable using ()
        enum t = true;
    else
        enum t = false;
}
void main() {
    void f(int i) {}
    t!f;
}