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Use one method definition for several types of classes

LDIL

Hello all.

The original problem is as follows. I have a method  which should accept both float number and integer, as well as anihter which is bar:

I only know how to the following:

defmethod( foo ( ( num fixum ) ( gro bar ) )

foo( float( num ) gro )

)

defmethod( foo ( ( num flonum ) ( gro bar ) )

.. code

)

Is there a way to have one method definition for both fixnum and flonum?

Also, is there a way to generalize this for any type of classes?

  • Andrew Beckett

    The way you would normally handle this would be to define the method for a common superclass of the classes involved. Of course, for user-defined classes, you are free to define the class hierarchy as you wish, with abstract classes in the hierarchy to achieve the grouping you wish.

    With the built-in types, there is already a common superclass of fixnum and flonum, which is called number: 

    subclassesOf(findClass('number))
    (class:fixnum class:flonum)

    So all you'd need to do is define:

    defmethod(foo ((num number) (gro bar))
       ; do something
    )

    There's no way to define a method to be specialised on more than one class (well, not without horrible use of custom specializers probably - I didn't think about it too hard). I wrote an article How to use custom specializers in SKILL++ methods to specialize on the objType of a database object from which the main conclusion I drew was that this should be used with extreme caution because it could be very hard to follow the flow of control if you deviate too far from the standard method dispatch.

    The right way is to specialize on a superclass, as I suggested above.

    Andrew.

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