On Fri, Nov 27, 2009 at 4:40 PM, Igor Stasenko <siguctua at gmail.com> wrote:

> 2009/11/28 Nicolas Cellier <nicolas.cellier.aka.nice at gmail.com>:
> > 2009/11/27 Eliot Miranda <eliot.miranda at gmail.com>:
> >> An approach I like is to add an endOfStreamValue inst var to Stream and
> >> answer its value when at end.  This way nil does not have to be the
> >> endOfStreamValue, for example -1 might be much more convenient for a
> binary
> >> stream, and streams can answer nil without confusing their clients.
>  atEnd
> >> can be implemented as
> >>     atEnd
> >>         ^self peek = self endOfStreamValue
> >> You can arrange to make streams raise an end-of-stream exception instead
> of
> >> the endOfStreamValue by using some convention on the contents of
> >> endOfStreamValue, such as if it is == to the stream itself (although I
> note
> >> that in the Teleplace image the exception EndOfStrean is defined bit not
> >> used).
> >>
> >> Of course, stream primitives get in the way of adding inst vars to
> stream
> >> classes ;)
> >> IMO this is a much more useful scheme than making nil the only
> endOfStream
> >> value.
> >>
> >
> > Last time I proposed to have an inst var endOfStreamAction was here
> >
> http://lists.gforge.inria.fr/pipermail/pharo-project/2009-June/009536.html
> > .
> > Abusing nil value -> nil, I could even let this inst var
> > un-initialized and be backward compatible
> > (initializing with a ValueHolder on nil would do as well)
> >
>
> Nicolas, have you considered introducing methods which allow
> graciously handle the end-of-stream while reading?
> Something like:
>
> nextIfAtEnd: aBlock
> and
> next: number ifAtEnd: aBlock
>
>
> then caller may choose to either write:
>
> char := stream nextIfAtEnd: [nil]
>
> or handle end of stream differently, like leaving the loop:
>
> char := stream nextIfAtEnd: [^ results]
>
> the benefit of such approach that code which reads the stream , don't
> needs to additionally
> test stream state (atEnd) in iteration between #next sends neither
> requires some unique value (like nil) returned by #next
> when reaching end of stream.
>

IMO the block creation is too expensive for streams.  The defaultHandler
approach for and EndOfStream exception is also too expensive.  The
endOfStreamValue inst var is a nice trade-off between flexibility,
efficiency and simplicity.  You can always write
     [(value := stream next) ~~ stream endOfStreamValue] whileTrue:
        [...do stuff...



>
> > Nicolas
> >
>
>
> --
> Best regards,
> Igor Stasenko AKA sig.
>
>
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