When you learn c + + read such code

 
Template 
The class SharedPointer; 

Template 
Auto swap (SharedPointer & LHS, SharedPointer & RHS) 
{
Using STD: : swap; 
Swap (LHS) PTR, RHS. PTR); 
Swap (LHS) ref_count, RHS. Ref_count); 
Swap (LHS. Deleter, RHS. Deleter); 
} 

If SharedPointer is normal class, then the forward declarations defined before, certainly not the use of its members, can only use it a pointer or reference, but why class template after forward declaration, definition, members will be able to use it?