On Monday, 23 July 2012 at 15:37:17 UTC, Simen Kjaeraas wrote:
On Mon, 23 Jul 2012 16:32:15 +0200, monarch_dodra
<[email protected]> wrote:
Is there any (efficient and correct) way to do ternary
comparison on two objects?
You know the:
----
if(a<b) return -1;
if(b<a) return 1;
return 0;
----
I'm using the above method in a template, and the problem is
that if a or b is a struct/class, this will resolve to 4 (!)
calls to opCmp.
First, no. It will only call opCmp twice - once for each
comparison. You're thinking of opEquals.
Hum. Fine. I though that if a and b were class, then there was
the same behavior. My bad.
But that's still twice too many calls.
Second, have you tried a.opCmp(b), cause that's the logical
thing to try, and it works.
It works but *if* the types are not equal, then this may or may
not be equivalent to b.opCmp(a).
Like other operator magic in D, it's not really magic. It's
just a simple lowering of a < b to a.opCmp(b) < 0.
In other words, operator overload functions in D can be called
just like regular functions:
This lowering only applies:
*If a.opCmp(b) and b.opCmp(a) resolve to the same function.
*Otherwise, exactly one of a.opCmp(b) and b.opCmp(a) must be
compilable.
I'd agree with a rewrite, but there are tricky edge cases. I
would have thought the language provided a ternary compare. If it
doesn't, I'd say it should. Preferably in std.functional?
