CODEWITHSUNDEEP
smalltalk
Leandro Caniglia
Leandro Caniglia

Reputation: 14858

How should super behave with instance-specific behavior?

Assume object is an instance of class C. Also assume that object has an instance-specific method m attached to it. The method m is defined in both C and its superclass C0. The question is, which method should the expression

super m

invoke when self == object, and why?

I see two possible answers:

  1. C >> #m (the method in the object class)
  2. C0 >> #m (the method in the object class superclass)

EDIT

Even though the way we implement instance-specific behavior shouldn't matter for the semantics of super, let me point out that my favorite implementation is the one that places the so called MethodDictionaryArray (or MDA for short) in object headers, instead of the object class. As you can imagine, a MDA contains the method dictionaries of the inheritance chain.

With this implementation you can put instance behavior in a new MethodDictionary (MD) and redefine the object's MDA as the nested array #{MD. MDA}.

Upvotes: 1

Views: 134

Answers (3)

Jim Sawyer
Jim Sawyer

Reputation: 143

It seems to me that one can phrase the definition a bit differently,
to get at the proper resolution of the semantics.

If we consider the normal case to be equivalent to

'do not include in the search any methods that are defined
 by the receiver, include only those which are inherited'

then the implementation details are not required
when we are deciding which answer to expect.

Upvotes: 0

David Buck
David Buck

Reputation: 2847

The standard definition of super is that super sends a message to the same receiver as self but starts the method lookup in the class above the one where the current method is defined.

Upvotes: 1

codefrau
codefrau

Reputation: 4623

IMHO it should invoke C0>>m to behave just like 'normal' instances of C. The implementation detail of how the instance-specific behavior is realized shouldn't matter. If you copy a method from C to its instance, it should ideally behave exactly the same as before.

Upvotes: 4

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