Xtreams question - OC of chars to String

I have a question about converting an OrderedCollection full of chars
into a string. [1]

I would have thought there was a method like #asString that could be
sent to an OrderedCollection to produce a string. I find myself having
to do the process in three steps: 1) #reading the OC; 2) creating an
empty string; and then, 3) iterating over every char to put it into the
String.

I think I'm missing a simpler way. Especially with Xtreams. Shouldn't I
just use a filter, change the #contentSpecies, or something?

Chris


[1]

startTag: data
     <action: 'element'>
     |tagdata str |
     tagdata := data second first reading.
     str := (String new: 20) writing.
     tagdata do: [:each| str put: each].
     ^'html ' , (data first second first asString) , $: , $' , (str
close; terminal) , $'

String withAll: yourCollection

as in...

String withAll: (#($a $b $c) asOrderedCollection)

I have a question about converting an OrderedCollection full of chars into a string. [1]

I would have thought there was a method like #asString that could be sent to an OrderedCollection to produce a string. I find myself having to do the process in three steps: 1) #reading the OC; 2) creating an empty string; and then, 3) iterating over every char to put it into the String.

I think I'm missing a simpler way. Especially with Xtreams. Shouldn't I just use a filter, change the #contentSpecies, or something?

Chris


[1]

startTag: data
    <action: 'element'>
    |tagdata str |
    tagdata := data second first reading.
    str := (String new: 20) writing.
    tagdata do: [:each| str put: each].
    ^'html ' , (data first second first asString) , $: , $' , (str close; terminal) , $'

The following works:

String withAll: #($a $b $c)

But I'm not sure I'm answering your question. 

Thank you Bob and Douglas. That's a nice simple solution that I was unfamiliar with. Perfect.

Happy New Year,
Chris

On Sat, 29 Dec 2012, Chris Cunnington wrote:

> I have a question about converting an OrderedCollection full of chars into a
> string. [1]

| oc |
oc := #($a $b $c) asOrderedCollection.
oc as: String.

>
> I would have thought there was a method like #asString that could be sent to
> an OrderedCollection to produce a string. I find myself having to do the
> process in three steps: 1) #reading the OC; 2) creating an empty string; and
> then, 3) iterating over every char to put it into the String.

Since the size of Strings (or an instance of a variable class in general)
can't be changed, therefore creating an empty String and concatenating to
it one character at a time is a bad pattern in Smalltalk. Your algorithm
will need O(n^2) time to finish (where n is the number of characters), and
you'll also waste O(n^2) space, which will make your code even slower,
since the intermediate collections will have to be garbage collected.


Levente

On 2012-12-29 1:47 PM, Levente Uzonyi wrote:
> On Sat, 29 Dec 2012, Chris Cunnington wrote:
>
>> I have a question about converting an OrderedCollection full of chars
>> into a string. [1]
>
> | oc |
> oc := #($a $b $c) asOrderedCollection.
> oc as: String.
>
Thanks. I rolled the versions forward and back to try them out. It's much slower
concatenating one character at a time. I figured there had to be a
better way, but wasn't seeing it.

Thanks,
Chris

On 29 December 2012 17:30, Chris Cunnington
<[hidden email]> wrote:
You're getting Characters, I guess, because you're reading one element
at a time [1]. There's nothing stopping you reading more than that:

('abc' reading read: 3) = 'abc'.
('abc reading rest) = 'abc'.

frank

[1] It's worth bearing in mind that Xtreams operate over streams of
arbitrary objects, not just characters.

On 2012-12-29 3:46 PM, Frank Shearar wrote: I don't know. The situation is more like:

     oc := #($a $b $c).
     oc := oc asOrderedCollection.
     oc reading read: 3   an OrderedCollection($a $b $c)


The terminal is the OC. But it returns an OC and I want a string from
the chars. I've been looking at the transforms page of the Xtreams docs
and that seems more about changing the encoding. I think my problem
wasn't really about Xtreams.

Chris

"Chris Cunnington"<[hidden email]> wrote:
Hm, I have to admit that collection streams should perhaps support overriding their contentsSpecies. As it is they assume it should be the same as that of their underlying collection. One might argue that terminal streams should stick to their primary purpose of accessing terminals rather than trying to support some types of conversions as well. But there already is a precedent of sorts in the external streams, so it's not entirely solid argument either.

Barring that, you could write instead of reading, which would allow you to control the type of the terminal collection.

        String new writing write: 'abcdefg' asOrderedCollection; close; terminal

The reading equivalent would be using the longer version of read where you pass in the target collection but you're then forced to handle the collection size explicitly which seems less elegant:

        oc :=  'abcdefg' asOrderedCollection.
        string := String new: oc size.
        oc reading read: oc size into: string.

It feels sort of like doing the job of the write stream above by hand. You could also use an identity transform that allows setting the contents species:

        ('abcdefg' asOrderedCollection reading collecting: [ :c | c ]) contentsSpecies: String; rest

But that again feels like more trouble than it's worth. I think that's about all that Xtreams have to offer here.

HTH,

Martin

On 2012-12-30 1:01 AM, [hidden email] wrote: That's pretty nifty. Perhaps I was reading when I should have been writing. Stacks and transforms came to mind with Xtreams: sending one kind of
content into another stream while changing the elements. This was I was
trying to reach for, but you first example looks the best.

Thanks,
Chris
>
> But that again feels like more trouble than it's worth. I think that's about all that Xtreams have to offer here.
>
> HTH,
>
> Martin
>
>

On Sat, Dec 29, 2012 at 12:30 PM, Chris Cunnington <[hidden email]> wrote:

I think I'm missing a simpler way. Especially with Xtreams. Shouldn't I just use a filter, change the #contentSpecies, or something?

Yeah, writing into an OrderedCollection with a stream is a bit suspect to begin with. Both provide a way to grow an underlying fix-size collection as you add more elements. If you have an OrderedCollection, you can just send #add:, no need for a write stream. If you want to build a string, "String new writing" will do the job, no need for an OrderedCollection. 

Also, you can write an OC full of characters directly into a write stream on a string:

chars := 'abc' asOrderedCollection.

String new writing 

write: '123';

write: chars; 

conclusion

Colin

Martin also made it look easier with a write than a read. I think I was looking at it the wrong way around. The OC shouldn't be the receiver but the argument. #writing into a String instead of #reading an OC.

Thanks,
Chris