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Re: operator overloading

by Warner Onstine-3 :: Rate this Message:

On 10/1/07, Tom Nichols <tmnichols@...> wrote:
> Ah, yes I see your issue. The > and < operators (comparison) assume that
> A < B OR B <= A will always be true. When you're talking about sets,
> A may not be a subset of B AND B might not be a subset of A. So I
> suppose the less than/ greater than does not really equate to subset
> notation. You could use leftShift and rightShift...

Unfortunately not quite the same (especially since you can have
subsets and proper subsets). Not to mention I think the notation is
unclear in the given context (which is what the DSL is all about
anyways).

There are of course other operators I could override, but the <=, <,
=>, > make the most sense to me given the context. At this point I've
put in a comment on http://jira.codehaus.org/browse/GROOVY-1889 in
hopes that we can get this in for Groovy 2.0. It hurts to be behind
Ruby in this way (heck, even C# allows you to override these methods
specifically).

Thanks for all the help, just sorry that I wasn't mistaken.

-warner

>
> Try this?
>
> class MySet {
> def items = []
> public boolean leftShift(other) {
> if( ! (other instanceof MySet) ) return false
> (this.items - other.items).size == 0
> }
>
> public boolean rightShift(other) {
> if( ! (other instanceof MySet) ) return -1
> (other.items - this.items).size == 0
> }
>
> public boolean equals( other ) {
> if( ! (other instanceof MySet) ) return -1
> (other.items - this.items).size == 0 &&
> (this.items - other.items).size == 0
> }
> }
>
> def set1 = new MySet( items:[1,2,3] )
> def set2 = new MySet( items:[1,2,3] )
> assert set1 == set2
> assert set1 << set2 && set2 << set1
> assert set1 >> set2 && set2 >> set1
>
> set2.items -= 3 //set2 == [1,2]
> assert set1 != set2
> assert set2 << set1 && set1 >> set2
> assert !(set1 << set2) && !(set2 >> set1)
>
> set3 = new MySet( items:[1,8] )
> assert !( set1 >> set3 ) && !( set3 >> set1 )
> assert !( set1 << set3 ) && !( set3 << set1 )
>
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--
Warner Onstine - Programmer/Author
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