Populate a new array.

Here's another one:

I've created a method that returns an array of its own class:

anArray: aQuantity
        | a |
        a := Array new: aQuantity.
        a size
                do: [:i | a at: i put: self class new].
        ^ a

but, for a while, I was trying to make this a single line:

^ (Array new: aQuantity) do: [:item | item := stuff ]

This doesn't work (I think) because "do" passes in a value rather than a  
reference. I didn't see how it could be done with withIndexDo: either.

Wondering if I'm missing something.

Also, observing that "at:" is actually implemented in Object, which  
seems...odd!
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On Mar 11, 2007, at 10:40 , Blake wrote:

^(1 to: aQuantity) collect: [:i | stuff]

- Bert -


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On Sun, 11 Mar 2007 04:30:29 -0800, Bert Freudenberg  
<[hidden email]> wrote:

> ^(1 to: aQuantity) collect: [:i | stuff]

Very nice, Bert, thanks!
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Blake wrote:

Here, you're constantly assigning the variable "item" to new values, so
the array remains untouched. I guess in a perfect world, the compiler
shouldn't allow assignment to block parameters... I'm surprised that the
Squeak compiler allows this.

> 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. It's not often useful (and downright dangerous if you ask me),
but I've used it before (for example) to serialize the state of any
object in an image.

Michael.

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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

- Bert -


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Bert Freudenberg wrote:


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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