Issue 15223: OCL 2.2 11.7.1 Why must + be commutative for Collection::sum() (ocl2-rtf)
Source: Model Driven Solutions (Dr. Edward Willink, ed(at)willink.me.uk)
Nature: Uncategorized Issue
Severity: 
Summary: Collection::sum() requires that its T::+() is commutative and associative.


Associativity is necessary for predictable results.


Commutativity is not necessary, most trivially for String::+ for which sum() could usefully
concatenate an OrderedSet.


Suggest: remove the requirement for commutativity.

Resolution: 
Revised Text: In 11.6.3 OrderedSet and 11.6.5 Sequence add
sum() : T
Redefines the Collection operation to remove the requirement for the + operation to be associative and/or
commutative, since the order of evaluation is well-defined by the iteration over an ordered collection.
Actions taken:
April 23, 2010: received issue
April 25, 2011: closed issue
Discussion: 
Yes. Introduction of String::+() as a shorthand for String::concat() makes the
suggestion a natural extension, but only for OrderedCollections.
No. Neither associativity nor commutativity is necessary for OrderedCollections
End of Annotations:=====
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Date: Fri, 23 Apr 2010 13:51:52 +0100
From: Ed Willink <ed@willink.me.uk>
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To: issues@omg.org
Subject: OCL 2.2 11.7.1 Why must + be commutative for Collection::sum()
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Hi


Collection::sum() requires that its T::+() is commutative and associative.


Associativity is necessary for predictable results.


Commutativity is not necessary, most trivially for String::+ for which sum() could usefully
concatenate an OrderedSet.


Suggest: remove the requirement for commutativity.


     Regards


        Ed Willink