Issue with unconstrained template-based approaches: Only static dispatch is possible which means, the compiler has to duplicate the procedure for all actual type-combinations and a procedure cannot return objects of different types, even though your are only interested in the interface they implement.
Well, you could if you either ensure, that the layout of the inherited part of a structure is the same for all structures, that inherit the same structure. Or you could return a tagged enum. However, with interfaces or traits, you just have to ensure that the table of interface/trait-methods of different types, that implement the same interface/trait. This table is constant and therefore a reference to it can be shared by every instance of the interface/trait.
Yes, it might be slower, because instead of direct method-calls, you have a layer of indirection, but you only need one copy of the method, not one for every type-combination. If all copies of this method have to fit in the L1-cache simultaneously but cannot, it might actually be faster.
Well, you could if you either ensure, that the layout of the inherited part of a structure is the same for all structures, that inherit the same structure. Or you could return a tagged enum. However, with interfaces or traits, you just have to ensure that the table of interface/trait-methods of different types, that implement the same interface/trait. This table is constant and therefore a reference to it can be shared by every instance of the interface/trait.
Yes, it might be slower, because instead of direct method-calls, you have a layer of indirection, but you only need one copy of the method, not one for every type-combination. If all copies of this method have to fit in the L1-cache simultaneously but cannot, it might actually be faster.