struct opCmp confustion

[Namespace]

>  A string is an array of chars. Structs and Classes have opCmp. 
> You could make a wrapper for the string to include the opCmp 
> then, but that seems irrelevant.
>
>  Although another option is to make a separate opCmp function 
> that would do it. Tested and works :)
>
> import std.algorithm;
>
>  //simple wrapper
>  int opCmp(string a, string b) {
>    return cmp(a,b);
>  }
>
>  unittest {
> 	assert("abc" < "efg");
> 	assert("efg" > "abc");
> 	assert("abc" == "abc");
>  }

Maybe I'm wrong but this method is never called by one of these 
compares. Or is this the point?
I wished many times that something like this work, even for other 
constructs. That would be a way to avoid nasty opCmp, opEquals 
and so on in the object.d.