How to declare function with the same call signature as another?

[Tofu Ninja via Digitalmars-d-learn]

I feel like this should be simple but I can't seem to figure it 
out. How do I declare a function to have the same call signature 
as another function/callable type?

Like if I have:

alias Sig = int function(int x, int y);

How do I define a function such that it will have the same call 
signature as Sig? How do I take into account all the extra stuff 
that can go into a function signature like the argument 
attributes and the return type attributes etc.?

Another way to phrase this question would be, how do I pass a 
function signature into a template and actually define functions 
with it?

Related question, if I have Sig, how would I define DeltaSig to 
be exactly the same as Sig but with an extra parameter at the 
start or end of the parameter list?

Thanks :)