[Pharo-users] Pharo 7 streams API

Sven Van Caekenberghe sven at stfx.eu
Sat Jun 23 12:53:36 EDT 2018


Peter,

> On 23 Jun 2018, at 15:39, Peter Uhnák <i.uhnak at gmail.com> wrote:
> 
> Hi,
> 
> I'm starting to familiarize myself with new streams, and one thing I've noticed is the removal of #lineEndConvention (which I use all the time).
> 
> So a statement like this
> 
> aFile writeStreamDo: [ :stream |
> 	stream lineEndConvention: #lf.
> 	stream << '...'
> ].
> 
> has to be written like so
> 
> aFile writeStreamDo: [ :rawStream | |stream|
> 	stream := (ZnNewLineWriterStream on: rawStream) forLf.
> 	stream << '...'
> ].
> 
> which feels very messy because I am mixing writing with the configuration. And I don't even take account for buffered/encoded decorators. Plus it increases the incidental complexity -- I need another variable, and I can accidentally write to the wrong stream, etc.
> 
> Would a method like #writeStream:do: (or #writeStreamTransform:do:) make sense? E.g.
> 
> aFile writeStreamTransform: [ :stream | (ZnNewLineWriterStream on: stream) ] do: [ :stream |
> 	stream << '...'
> ]
> 
> To separate the composition from the usage?
> 
> Thanks,
> Peter

The goals of the 'new' (they have existed for quite a while) streams is to go from single big complex do all classes and replace that with a composition of much simpler single purpose classes. Another goal is to reduce the API so that it becomes easier to create new stream classes. Of course, a consequence is that you need composition to get the functionality you want. But I think you understand the tradeoff.

If the mixing of configuration/setup with writing/reading bothers you, then I would suggest using two methods. One that does only the writing/reading assuming a limited API, and another that does the configuration/setup, using composition.

Note that the streams that you get already are a composition (most often a BinaryFileStream wrapped in a Buffered stream wrapped in a Encoding/Decoding stream). EOL translation is not a standard part of that. But there is quite some system code that does uses EOL translation.

Sven





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