Hi Stef,

potentially interesting sidenote: #veryDeepCopy works correctly because it forces a rehash (see Object>>#veryDeepCopyWith: at the bottom).

Cheers,
Patrick
________________________________________
From: Squeak-dev <squeak-dev-bounces at lists.squeakfoundation.org> on behalf of Stéphane Rollandin <lecteur at zogotounga.net>
Sent: Friday, March 3, 2023 4:39:43 PM
To: liste [Squeak-dev]
Subject: [squeak-dev] #deepCopy seems broken for IdentitySet

Hello all,

After spending way too long on a bug in my code, I found the culprit to
be that deep-copying an IdentitySet is not reliable. The copy may need a
#rehash.

To see this, do

        iset := {1 at 1} asIdentitySet.
        results := Set new.

        100 timesRepeat: [
                dcset := iset deepCopy.
                results add: (dcset includes: dcset anyOne)].

        results "explore it"

This should show both true and false in results.

The proportion is about 2/3 false, which seems to correspond to the
probability that #scanFor: will return a wrong index for a set of one
element that needs a rehash, since

        {1 at 1} asIdentitySet array

may be either one of

        {nil . nil . 1 at 1}
        {nil . 1 at 1 . nil}
        {1 at 1 . nil . nil}


This behavior has been there for ages though - so, am I missing something?

Stef