equivariant functions

[Andrei Alexandrescu]

Steven Schveighoffer wrote:
> What about returning a member?  i.e.:
> 
> inout(typeof(s.ptr)) getptr(inout const(char)[] s) { return s.ptr;}

Yah there is a recurring problem - we need to find a notation that works 
nicely and expressively for member functions as well as free functions.

For free functions an easy-to-explain-and-understand way is to have 
"inout" mark the incoming / outgoing TYPE entirely, not only its 
qualifier. Then:

inout stripl(inout const(char)[] s);

means: accept any subtype of const(char)[] and call that type "inout" in 
the return type. Then it's easy to access dependent stuff:

typeof(inout.ptr) at(inout const(char)[] s);

Notice that for one-parameter functions there's not even a need to 
specify the inout in the argument list because it's unambiguous:

inout stripl(const(char)[] s);
typeof(inout.ptr) at(const(char)[] s);

When you get into member functions things aren't quite nice:

class A
{
     private int a;
     inout clone() inout; // ehm
     typeof(&inout.a) getPtrToA() inout; // ehm
}

> is that what you had in mind?
> 
> this syntax is going to be used often, since it's what you would use for an 
> accessor.  So it should be simple to understand if possible.

Yah I agree. At this point I don't have any solid solution for 
notation... please continue rolling out ideas.


Andrei