Overload of ! operator

[monarch_dodra]

On Wednesday, 26 June 2013 at 05:29:49 UTC, Jonathan M Davis 
wrote:
> On Wednesday, June 26, 2013 07:15:19 Eric wrote:
>> I should have also added that the overloaded ! method returns a
>> class instance and not a bool.
>
> Well, at that point, you're completely out of luck with regards 
> to overloading
> !. In general, D doesn't really support overloading operators 
> in a manner that
> doesn't match how the built-in types work. It does things like 
> assume that <,
> <=, >=, and > will act the same way that they do with the 
> built-in types and
> uses opCmp to extrapolate all of those operators. In some 
> cases, you _can_
> make overloaded operators return types that make it so that 
> they don't
> function anything like the built-in types (e.g. opBinary with + 
> could return a
> completely unrelated type that had nothing to do with the 
> original type or
> with addition), but in pretty much any case where the compiler 
> can get away
> with using the same overloaded operator for multiple operators, 
> it does it.
> So, a number of decisions were made to better support 
> correctness with types
> that actually try and overload operators to match what the 
> built-in types do
> without caring about how that would affect types that would try 
> and overload
> them to do unrelated stuff.
>
> - Jonathan M Davis

Yeah, basically, you define:
* opCast(bool) //to test both "true" and "false"
* opEqual //test equality (both == and !=)
* opCmp //Comparison (< > <= >=)

And everything gets defined from these. It also works that way 
for operators:
op++ is defined in terms or ++op.
And if you define "op+", then defining op++ becomes entirely 
optional!

This is a cool feature, although there are those *very* rare 
cases where it gets in your way.

For example, the other day, I was trying to implement a "tribool":
http://www.boost.org/doc/libs/1_53_0/doc/html/tribool/tutorial.html

It did not work, I mean: AT ALL!

This is because for a tribool, being "not true" does not imply 
being "false"...