Bert Freudenberg wrote:
On Mar 15, 2007, at 10:54 , Michael van der Gulik wrote:
Also, observing that "at:" is actually implemented in Object,
which seems...odd!
It is a bit odd. An Object in the virtual machine resembles an array
of instance variables, and that method assigns to an instance
variable by number.
Wrong. Any Squeak object is made of zero or more instance variables
("named variables") plus zero or more numbered variables ("indexed
variables"). The difference is that the number of named variables is
fixed for all objects of that class, but the number of indexed
variables can be specified when creating an instance using #new:, so
it can differ from instance to instance. Object>>at: lets you access
those indexed variables. How else would you access these?
It's not often useful (and downright dangerous if you ask me)
Huh? It provides the very basics of the system! If we Smalltalkers
say "everything is an Object" we mean it. Literally. There is no
special "array object" that is different from "regular objects".
Rather, you can implement an array as an object that happens to have
indexed variables:
Object variableSubclass: #BertsArray
instanceVariableNames: ''
classVariableNames: ''
poolDictionaries: ''
category: 'Bert-Arrays'.
(BertsArray new: 7) at: 5 put: 42
Thanks, Bert. I can't believe I've been Smalltalking for so many years
and not known that! I always just assumed that arrays were some special
case handled by the VM, like SmallIntegers.
Michael.
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