With Camille we spent some minutes introducing a weak slot. A weak slot with a weak reference i.e., it is not taken into account by the garbage collector. If an object is only referenced by weak references it will be garbage collected. The nice thing about this is that now we can mix transparently weak and non-weak slots inside the same object. For example: Object subclass: #MyWeakThingy slots: { #weakLala => WeakSlot. #normalInstVar } classVariables: { } category: 'SlotTestGuille' weakLala: someLala weakLala:= someLala weakLala ^ weakLala weak := MyWeakThingy new. o:= Object new. weak weakLala. "=>Object new" o :=nil. weak weakLala. "=>nil" We also implemented with Camille the #emit* methods to make it a bit faster. A simple benchmark in my machine shows that "With no optimizations" [weak weakLala:o] bench "14,338,031 per second" "With optimizations" [weak weakLala:o] bench "27,955,761 per second" "A normal array access" someArray := Array new: 1. [someArray at: 1 put: o] bench "'39,609,322 per second'" We commited it into the inbox, the issue is the following: https://pharo.fogbugz.com/f/cases/14998/Add-WeakSlot Camille & Guille