opCmp

[Daniel Murphy]

Bug!

"Ali Çehreli" <acehreli at yahoo.com> wrote in message 
news:jgh2nb$rtv$1 at digitalmars.com...
> On 02/03/2012 06:44 AM, Gor Gyolchanyan wrote:
> > Good day.
> >
> > There's a problem in how opCmp works.
> >
> > I have a structure, that represents an element of a range. Let's say a
> > character. That character can be invalid.
> > I need all comparison operators to return false of at least one of the
> > operands is invalid.
>
> As an observation, you want to implement the concept of "unordered" for 
> types, similar to floating point types:
>
>   http://dlang.org/expression.html#floating_point_comparisons
>
> I am very surprised that the following operator works with 
> non-floating-point types:
>
> class C
> {
>     override int opCmp(Object o)
>     {
>         return 0;
>     }
> }
>
> void main()
> {
>     auto c = new C;
>     auto b = (c !<>= c);      // <-- compiles!
>
>     int i, j;
>     auto b2 = (i !<>= j);     // <-- compiles!
> }
>
> Is that supported? Is it a bug? Would using those /unordered/ operator 
> help in your case?
>
> > with opCmp, the expression a @ b is rewritten as a.opCmp(B) @ 0, which
> > doesn't allow me to define such a logic.
> > wouldn't it be better to change the rewrite of opCmp to test for exact
> > values -1, 0 and 1? In that case I could return 2 and have all
> > comparisons fail.
> >
>
> Ali
>