Experimental Physics and
Industrial Control System

Marty Kraimer <[email protected]> · Wed, 28 Sep 2005 08:06:48 -0500

Jeff Hill wrote:

Please pardon an internal debate converted to a mail message :-)

Use 'assign' instead of 'operator =',
'isEqual' instead of 'operator ==',

Shouldn't this also apply to dataAccess? {Or should I say :-) }

PropertyCatalog currently has "operator =" and "operator ==".

O Do they meet the conventional wisdom test? That is, is their purpose
roughly equivalent to the purpose of these operators with primitive types? I
Originally I thought yes, but I have thought about this further and its
probably more accurate to call 'operator =' "extract what's in the LHS from
the RHS", and what 'operator ==' does "return true if everything in the LHS

is equivalent in the RHS".

Should  == (or equals) always guarantee that it is an equivalence relation?

That is

1) reflexive =>  x==x is always true
2) symetric  => if x==y then y==x
3) transitive => if x==y and y==z then x==z

Java states that if a class overrides equals it should gurantee that its

implementation is an equivalence relation.

I suspect similar advice appears somewhere for C++.

dataAccess == does not appear to be  symetric

If containers are implemented for

struct A { int x; int y} and struct B {int x; int y; int z}

Then won't the following happen if A.x=B.x and A.y=B.y?

A==B is true but B==A is false

Marty

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System