Re: Real OO

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

Norman H. Cohen writes
> No flexibility is being traded off.  Your phrase "optimzation by the
> developer" conjures up images of programs made inflexible and inscrutable
> to improve efficiency, but that is not required with the Ada mechanism.

Inflexible and insrcutable are not necessarily related.

> All that is required is that, in a context where Rect1 and Rect2 are
> known to both have dynamic type Rectangle_Type, Rect1 and Rect2 should be
> declared to be of type Rectangle_Type rather than Shape_Type'Class.  Then
> the call Corresponding_Parts_Equal(Rect1, Rect2) is resolved statically
> rather than dynamically.  If anything, this increases the
> understandability of the code.

The question is not whether it is better to use Rectangle_Type instead of  
Shape_Type'Class, but whether it is better to use Rectangle_Type'Class  
instead of Rectangle_Type.

Static resolution makes it impossible to safely attach a more specific  
rectangle object to Rect1 or Rect2, so you do sacrifice flexibility.  Why  
decide in advance that your code, when inherited by a subclass, will ignore  
that subclass' redefinitions of some (or all) of the routines?  It is hard  
enough to write classes that can be easily refined through inheritance (which  
ability is one of O-O's most advertized selling points) with dynamic binding;  
static binding makes it that much harder.

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

[comp.lang.eiffel readers will have seen this message before; sorry about  
that -- Jacob]