How to "extend" built-in types

[Dan]

On Friday, 26 October 2012 at 13:55:35 UTC, simendsjo wrote:
> Not sure if this is a bug or intended behavior:
> ...
> So.. What do I need to implement for a struct to be a valid
> built-in type?
> All valid properties (min, max etc) and operators for that type?

I am looking for something similar. I ended up looking at Proxy 
in typecons because the description says "// Enable operations 
that original type has". So for instance it looks like you could 
wrap an int or double in a struct and it is almost exactly like 
an int or a double. Presumably you could then overload just the 
changes (min/max for range, etc). I've found issues for my case, 
but at least its worth a look.

http://forum.dlang.org/post/ycayokcwncqfwfstomck@forum.dlang.org

If I try to check that this struct is numeric, unfortunately it 
is not.
     writeln("Is numeric ", isNumeric!CcRate); // false
     writeln("Is numeric ", isNumeric!double); // true


-----
struct CcRate {
   private double rate = 0;
   mixin Proxy!rate;

   this(double rate) {
     this.rate = rate;
   }
}
----

Thanks
Dan