Re: Overloading comparison operators

> I'm experimenting with a kind of query language. In this language,
> arithmetic and logical expression shall result in a description of the
> expression, not in the result of the actual expression evaluation itself.
> Hence the operator method should be able to return something at will and not
> be restricted to a certain result type.
>
> Just as an example, think of the following.
>
> (A op B) results in: new Operation(A,B,'op')
>
> With arithmetic operators, this works perfectly using an operator method
> like this:
>
> def plus(otherValue)  { new Operation(this,otherValue,'plus') }
>
> or in a generic way:
>
> def invokeMethod(String name, Object args) {
>     if (args.size()==1) { return new Operation(this,args[0]),name) }
>     ...
> }
>
> With Groovy's comparison operators there is currently no chance to do
> something like that.
>
> -Jörg
>
>
> 2008/7/17 Guillaume Laforge <glaforge@...>:
>>
>> By the way, I'd be curious to know what you have in mind?
>> What kind of DSL you would write with these operators?
>>
>> On Thu, Jul 17, 2008 at 11:03 AM, Jörg Staudemeyer
>> <jstaudemeyer@...> wrote:
>> > Hi
>> >
>> > are there any plans to change handling of comparison operators in a
>> > later
>> > version of Groovy?
>> >
>> > Currently, comparison operators only apply to classes that implement the
>> > Comparable interface and are mapped to the compareTo() method.
>> > compareTo()
>> > method must return an integer value, as dictated by the interface, but
>> > the
>> > result of a comparison expression is always boolean.
>> >
>> > IMO this is not consistent with handling of other operators like + and
>> > <<
>> > that always map to a specific method returning an arbitrary result
>> > value. As
>> > a result, usage of comparison operators in DSLs is quite restricted.
>> >
>> > What I would like to have is something like this:
>> >
>> > a < b  ==> a.smallerThan(b)
>> > a =<b ==> a.smallerThanEqualOrEqualTo(b)
>> > a!=b ==> a.notEqualTo(b)
>> >
>> > and so on. All this methods should normally return a boolean value, but
>> > in
>> > certain circumstances, like in a DSL, can also return something else.
>> >
>> > Implement this should not be particularly difficult, one could simply
>> > create
>> > default implementations of these methods for Comparable in
>> > DefaultGroovyMethods doing something constistent with current behaviour.
>> >
>> > What do you think?
>> >
>> > -Jörg
>> >
>> >
>>
>>
>>
>> --
>> Guillaume Laforge
>> Groovy Project Manager
>> G2One, Inc. Vice-President Technology
>> http://www.g2one.com
>>
>> ---------------------------------------------------------------------
>> To unsubscribe from this list, please visit:
>>
>>    http://xircles.codehaus.org/manage_email
>>
>>
>
>
>
> --
> A Groovy user