Re: Real OO

[Jacob Gore <jacob.gore@enmu.edu>]

Norman H. Cohen writes
> What does Eiffel do in the case of a call like
> A.Corresponding_Parts_Equal(B) where A and B have different dynamic
> types, but the version of Corresponding_Parts_Equal for the dynamic type
> of A expects the parameter to be of (or descendended from) the dynamic
> type of Current?

You would declare the function corresponding_parts_equal as follows:

corresponding_parts_equal(other: like Current): BOOLEAN is ...

This can appear in the text of A's class, or in the text of a class that A's  
class inherits (directly or indirectly).  "other: like Current" means that  
the static type of `other' is Current's (in your example, A's) class.

For example, suppose class Z inherits from class Y, which inherits from class  
X, where the function corresponding_parts_equal is defined (and neither Y nor  
Z redefine it).  The above declaration, as inherited by Z, is shorthand for  
the redefinition

corresponding_parts_equal(other: Z): BOOLEAN is ... same body.

That means that `other' can be an object of class Z or any of its subclasses.

This does what you asked, doesn't it?

Jacob
---
Jacob Gore, Eastern NM U.   Jacob.Gore@ENMU.Edu | Jacob@ToolCASE.Com