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Streaming on all collections

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Damien Cassou-3

Streaming on all collections

Hello,

why isn't it possible to stream over OrderedCollections ?

stream := WriteStream on: OrderedCollection new.
stream nextPut: $a

this generates a 'attempt to index non-existent element in an ordered
collection'

The documentation of WriteStream>>nextPut: says :

«
Fail if the collection of this stream is not an Array or a String.
»

Can somebody explain me why it is forbidden ?

--
Damien Cassou

Jon Hylands

Re: Streaming on all collections

On Sun, 11 Feb 2007 18:00:10 +0100, Damien Cassou
<[hidden email]> wrote:

> why isn't it possible to stream over OrderedCollections ?

You can only add elements to an OrderedCollection by using #add: (or one of
its variants). WriteStream assumes that if you send #new: to the class of
the collection it is streaming over, you can then say #at: index put:
value, where index <= the collections size.

If you want to do this, use Array.

stream := WriteStream on: Array new.
stream nextPut: $a

Later,
Jon

--------------------------------------------------------------
Jon Hylands [hidden email] http://www.huv.com/jon

Project: Micro Raptor (Small Biped Velociraptor Robot)
http://www.huv.com/blog

Damien Cassou-3

Re: Streaming on all collections

Jon Hylands a écrit :
> On Sun, 11 Feb 2007 18:00:10 +0100, Damien Cassou
> <[hidden email]> wrote:
>
>> why isn't it possible to stream over OrderedCollections ?
>
> You can only add elements to an OrderedCollection by using #add: (or one of
> its variants). WriteStream assumes that if you send #new: to the class of
> the collection it is streaming over, you can then say #at: index put:
> value, where index <= the collections size.

Sorry, I was not clear enough. I'm not talking about implementation
details, but about semantic of streams. I don't understand why
WriteStreams would not deal with all kind of sequenceable collections.

--
Damien Cassou

Klaus D. Witzel

Re: Streaming on all collections

Hi Damien,

on Sun, 11 Feb 2007 21:11:22 +0100, you wrote:

> Jon Hylands a écrit :
>> On Sun, 11 Feb 2007 18:00:10 +0100, Damien Cassou
>> <[hidden email]> wrote:
>>
>>> why isn't it possible to stream over OrderedCollections ?
>> You can only add elements to an OrderedCollection by using #add: (or
>> one of
>> its variants). WriteStream assumes that if you send #new: to the class
>> of
>> the collection it is streaming over, you can then say #at: index put:
>> value, where index <= the collections size.
>
> Sorry, I was not clear enough. I'm not talking about implementation
> details, but about semantic of streams. I don't understand why
> WriteStreams would not deal with all kind of sequenceable collections.

You are right, insofar as the class comments of Stream,
PositionableStream, ReadStream and WriteStream talk about a *sequence* (of
stream operations, IMO).

But only (sub-)instances of ArrayedCollection provide a *fixed* range of
integers as external keys.

In contrast to that, OrderedCollection has also integers as externals key,
but not a fixed range of them: the range *varies* with the size of the
instance.

A simulation of ArrayedCollection can be

(1 to: 6) asOrderedCollection writeStream nextPutAll: 'string'; contents

/Klaus

>

Alan L. Lovejoy

RE: Streaming on all collections

In reply to this post by Damien Cassou-3

<Damien Cassou>
why isn't it possible to stream over OrderedCollections ?

stream := WriteStream on: OrderedCollection new.
stream nextPut: $a

this generates a 'attempt to index non-existent element in an ordered
collection'
</Damien Cassou>

In VisualWorks, the following code "does the right thing":

(WriteStream on: OrderedCollection new)
nextPut: $H;
nextPut: $e;
nextPut: $l;
nextPut: $l;
nextPut: $o;
nextPut: $ ;
nextPut: $W;
nextPut: $o;
nextPut: $r;
nextPut: $l;
nextPut: $d;
nextPut: $!;
contents

I fail to grok why Squeak should not do likewise.

--Alan

P.S. Dolphin works (or rather, fails to work) just like Squeak in this
regard.

Jon Hylands

Re: Streaming on all collections

In reply to this post by Damien Cassou-3

On Sun, 11 Feb 2007 12:46:54 -0800, "Alan Lovejoy"
<[hidden email]> wrote:

> In VisualWorks, the following code "does the right thing":

The reason it works in VW is that #growToAtLeast: sets lastIndex to the
size the collection has grown, whereas in Squeak it keeps it at the current
position.

Later,
Jon

--------------------------------------------------------------
Jon Hylands [hidden email] http://www.huv.com/jon

Project: Micro Raptor (Small Biped Velociraptor Robot)
http://www.huv.com/blog

Philippe Marschall

Re: Streaming on all collections

In reply to this post by Damien Cassou-3

2007/2/11, Alan Lovejoy <[hidden email]>:

> <Damien Cassou>
> why isn't it possible to stream over OrderedCollections ?
>
> stream := WriteStream on: OrderedCollection new.
> stream nextPut: $a
>
> this generates a 'attempt to index non-existent element in an ordered
> collection'
> </Damien Cassou>
>
> In VisualWorks, the following code "does the right thing":
>
> (WriteStream on: OrderedCollection new)
> nextPut: $H;
> nextPut: $e;
> nextPut: $l;
> nextPut: $l;
> nextPut: $o;
> nextPut: $ ;
> nextPut: $W;
> nextPut: $o;
> nextPut: $r;
> nextPut: $l;
> nextPut: $d;
> nextPut: $!;
> contents
>
> I fail to grok why Squeak should not do likewise.
>
> --Alan
>
> P.S. Dolphin works (or rather, fails to work) just like Squeak in this
> regard.

The same as GST. Smalltalk/X however "does the right thing" as well.

Philippe

Alan L. Lovejoy

RE: Streaming on all collections

In reply to this post by Jon Hylands

<Jon Hylands>
The reason it works in VW is that #growToAtLeast: sets lastIndex to the size
the collection has grown, whereas in Squeak it keeps it at the current
position.
<Jon Hylands>

I'd explain it differently: Around the time of VW 1.0, someone at ParcPlace
put a lot of effort into rigourously making the Collection classes
intelligently distinguish between the concept of a collection's #size (its
logical size, the number of elements it contains logically) a a collection's
#capacity (its physical size, the number of slots it has allocated in which
elements could be stored.)

In VW, a Collection responds to #growToAtLeast: by increasing its logical
size. In Squeak, a Collection responds to #growToAtLeast: by increasing its
physical size--which in some, but not all cases, also increases the
Collection's logical size. Unfortunately, for OrderedCollections the
distinction between logical size and physical size (capacity) actually
matters.

--Alan

Klaus D. Witzel

Re: Streaming on all collections

In reply to this post by Jon Hylands

Thank you Alan, good background info.

Separating #capacity from #size is very intuitive.

/Klaus

On Sun, 11 Feb 2007 22:49:29 +0100, Alan Lovejoy wrote:

> <Jon Hylands>
> The reason it works in VW is that #growToAtLeast: sets lastIndex to the
> size
> the collection has grown, whereas in Squeak it keeps it at the current
> position.
> <Jon Hylands>
>
> I'd explain it differently: Around the time of VW 1.0, someone at
> ParcPlace
> put a lot of effort into rigourously making the Collection classes
> intelligently distinguish between the concept of a collection's #size
> (its
> logical size, the number of elements it contains logically) a a
> collection's
> #capacity (its physical size, the number of slots it has allocated in
> which
> elements could be stored.)
>
> In VW, a Collection responds to #growToAtLeast: by increasing its logical
> size. In Squeak, a Collection responds to #growToAtLeast: by increasing
> its
> physical size--which in some, but not all cases, also increases the
> Collection's logical size. Unfortunately, for OrderedCollections the
> distinction between logical size and physical size (capacity) actually
> matters.
>
> --Alan
>
>
>
>