Question

Why doesn’t the compiler find a match for read1? I don’t see the difference between read1 and read2; is there a limitation for nested typedef templates like the one in the Foo class?

template<typename T>
class Handle{};

class Foo{
public:
    typedef Handle<Foo> Handle;
};


template<typename T>
void read1(typename T::Handle){}

template<typename T>
void read2(Handle<T>){}


int main(int argc, char** argv)
{
    Foo::Handle f1;    
    read1(f1);

    Foo::Handle f2;
    read2(f2);
}

G++ compiler output, (G++ 4.4.5)

g++ -c -I.  main1.cpp 
main1.cpp: In function ‘int main(int, char**)’:
main1.cpp:37: error: no matching function for call to ‘read1(Handle<Foo>&)’

Answer 1

Foo::Handle f1;    
read1(f1);

The type being passed to read1 is Handle<Foo>, not Foo.

Templates are not inheritance. Handle<Foo> is a distinct class that is not a Foo, so there is no Handle<Foo>::Handle.