At 09:01 AM 1/15/2007 +0100, Paolo Bonzini wrote:
If the value of
receiver == comparand
is true then the receiver and comparand must have equivalent
identity hash values. Or more formally:
receiver == comparand ==>
receiver identityHash = comparand identityHash
This is not an "if and only if". If two objects have the same
identityHash you cannot conclude that they are identical. In GNU
Smalltalk "x identityHash identityHash == x identityHash" in particular,
so every object's identityHash will collide with exactly one integer's
identityHash.
This was the question that I needed an answer for. I saw that the spec in
the ANSI document and it didn't match the behavior exhibited. Nor did it
match the behavior in Squeak or VW either. I figured that something else
must be used to distinguish objects because primitives are used instead of
just a comparison of identityHashes.
Also note that "51546 asOop" is an error, while "51546 identityHash" is
the integer 51546 itself.
In the other case, (123/3) is the integer 41 rather than the fraction
(41/1), so
123 / 3 identityHash = 123 / (3 identityHash) = 123 / 3 = 41
(123 / 3) identityHash = 41 identityHash = 41
(123 / 3) asFraction identityHash = (41/1) identityHash = an object index
^^^^^^
this represents a Fraction object, not the value of 41/1
Paolo
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