🚀 go-pugleaf

On Wed, 19 Jun 2002 23:12:14 +0100, "Coho (Richard Swain)"
<vibron@krang.f9.co.uk> wrote:

>> almost need to create a new interface:
>> 
>> interface ThingThatDoesIntf1AndIntf2 {
>>     Intf1 getIntf1();
>>     intf2 getIntf2();
>> }
>> 
>> Except that you can't even pass this object round to a method that
>> expects to be given an Intf1 or an Intf2.
>
>But I don't see how using somekind of namespace resolution is 
>polymorphic either. i.e to specify which method to call you *have*
>to specify the interface the method is on. IMHO getIntfN() does that 
>just as well as some kind of language trick.
>
Me neither. Perhaps the best approach is to use a convention like:
    public void intf1_draw()...
    public void intf2_draw()...
but I don't think people are likely to adopt it.

>You are right about specifying a new interface, but I would hope that 
>practically all concrete classes are expressions of interfaces - to 
>which those two methods can be added.
>
>If a method takes a particular interface intf1 say you can always do
>
>theMethod( myclass.getIntf1() );
>
That's not too bad. Except that there's no way to get back from the
Intf1 to the original myClass object. I'm not sure you should ever
want to, but I still feel alienated by this somehow.

>and within that if you need to get hold of the other interface just do
>
>    Intf2 f2 = ((ThingThatDoesIntf1AndIntf2)fi).getIntf2();
>
>For your last point. If a method takes an object of type intf1 *or* 
>intf2 I'm not quite sure how it suppose to know which X() is the one to 
>be called internally unless they they are functionally equivalent and 
>hence the same method, or unless the object being passed in is only an 
>implementation of one of the interfaces, in which case no specific 
>resolution is required.

Bad wording on my part. I meant  "a method that expects to be given an
Intf1 or a method that expects to be given an Intf2."

I just don't think there's a really good solution, but as others have
pointed out, it fortunately doesn't arise very often.

Steve