[Pharo-dev] In-memory FileSystem write streams not being polymorphic

Nicolas Cellier nicolas.cellier.aka.nice at gmail.com
Wed Nov 13 16:32:14 EST 2013


Chris,
I have to completely disagree.
The idea of breaking a complex object into simpler parts is not just
theories and extremism.
Assigning several roles to an object is sometimes convenient for a start,
but generally does scale very badly.
It's a collective experience driven by pragmatic considerations in
developping in all sort of languages.
And it's my own experience too.

A file is like the container, the stream is about reading/writing the
contents.
I think I remember the confusion was made at the beginning in st-80,
because it was simple enough at that time.
So it's rather an historical slag, not something that was added later for
this special case.
And it is something that should have been revised, because when we added
pipes, sockets or other external streams, that ruined the idea of confusing
the two things into a not well delimited blob without clear
responsibilities.
Though we kept the original implementation and started to distort the
package by adding faked polymorphism like name ^'john doe'.

Clearly, I need no stream on its contents to rename a file, query its
permissions, or delete it, so why bother with internal states of a stream
if I'm interested in handling the file?
If I am interested about the contents, I don't need to ever know about the
path of the file nor its name, or shall I change a $A read from it into a
$B if the file is named 'turnAllAinB'?

Where exactly are we going to need this encapsulated blob which pretend to
be both a file and a stream? I would be happy to show that a rewrite is
both simple and good looking at end application sites.
Of course, inside the lava of multi year hacked stream hierarchy, it might
be a bit less obvious to disentangle the spaghetti.
Hence more radical solutions: table rase and complete rewrite.





2013/11/13 Chris Muller <asqueaker at gmail.com>

> On Wed, Nov 13, 2013 at 1:17 PM, Nicolas Cellier
> <nicolas.cellier.aka.nice at gmail.com> wrote:
> > Exactly, every specialized stream has its specialized API and/or
> specialized
> > implementation.
> > File streams don't even have a name, because they need not to.
> > You can browse XTFileReadStream and XTFileWriteStream, you won't find
> such
> > thing.
> > The file has a name, the stream does not need any.
> > Before adding anything to a stream, ask first, why am i going to need
> this?
>
> I agree with what Frank said, but not your suggestion that:
>
> > File streams don't even have a name, because they need not to.
> > If it really need it, the application certainly can retrieve the name
> from a higher level object (a
> > FIleReference, FileDirectory or whatever).
>
> because doing that means the FileStream is no longer
> fully-encapsulated.  And now for the same method to support a
> non-FileStream stream, what will be passed as the new FileReference
> argument?  nil?  So the code went from stream-delegation to
> case-logic.
>
> This is why organic growth happened in the original Stream hierarchy
> -- because it was "needed", not random.  Not strict, yes, but not
> "random" either.
>
> One final thing to consider about selector "uniformity" is how it can
> negate the ability to effectively trace code (via senders and
> implementors).  Wow, how many senders of #next...?
>
> Stream-composition is cool, though, and I understand that to be a
> benefit of the stricter API.
>
>
>
> > 2013/11/13 Frank Shearar <frank.shearar at gmail.com>
> >>
> >> On 13 November 2013 16:48, Chris Muller <asqueaker at gmail.com> wrote:
> >> > I know nothing about Xtreams but, IMO, this obsession with sterility
> >> > borders on mental illness.
> >> >
> >> > "All sort of un-needed complexity?"  That's overstating it a bit,
> >> > don't you think?
> >> >
> >> > So you must really feel stressed that ALL Object's, in fact, have a
> >> > #name, huh?  I admit this seems to push the limits but...
> >> >
> >> > what's the point of having any kind of different streams at all then?
> >> > It's the _differences_ between them that makes composing them useful.
> >> > Compression, encryption, filtering, sockets, files, circular, etc.
> >> > You think you'll be able to do all that and get away with all of them
> >> > having exactly the same API?
> >>
> >> They don't have the same API. And they shouldn't. And that's Nicolas'
> >> whole point. A Stream does not have a name (nor should it - what's the
> >> name of the compressed output of an audio stream from your
> >> microphone?). A FileStream can extend this API, and that's fine. But
> >> keep that out of the Stream API.
> >>
> >> So Nicolas is arguing that _difference_ should be reflected in the
> >> API. File streams have names, but generic streams do not.
> >>
> >> As it happens, Xtreams takes a very disciplined approach to this. Some
> >> streams have positions, and so you can go back. Some can't. This is
> >> reflected in the API. This is good.
> >>
> >> > IMHO working around that, passing extra objects around, sounds more
> >> > stressful than letting a stream on a _file_ know its filename..
> >>
> >> Mu. Streams have no names. File streams have names.
> >>
> >> frank
> >>
> >> >> If it really need it, the application certainly can retrieve the name
> >> >> from a higher level object (a FIleReference, FileDirectory or
> whatever).
> >> >
> >> > How does that solution allow uniformity in stream-using code?
> >> >
> >> > On Wed, Nov 13, 2013 at 9:58 AM, Nicolas Cellier
> >> > <nicolas.cellier.aka.nice at gmail.com> wrote:
> >> >> Yes, a Wrapper would provide the legacy API.
> >> >>
> >> >> And yes, the name of a stream should better not be part of the API.
> >> >> Most stream don't have a name, and adding such API adds all sort of
> >> >> un-needed complexity.
> >> >> It's an internal detail that can eventually help for reporting error
> if
> >> >> accessible, but nothing more.
> >> >>
> >> >> If it really need it, the application certainly can retrieve the name
> >> >> from a
> >> >> higher level object (a FIleReference, FileDirectory or whatever).
> >> >>
> >> >>
> >> >> 2013/11/13 Chris Muller <asqueaker at gmail.com>
> >> >>>
> >> >>> On Tue, Nov 12, 2013 at 7:31 AM, Nicolas Cellier
> >> >>> <nicolas.cellier.aka.nice at gmail.com> wrote:
> >> >>> > It's just a matter of selecting a strategy. I've proposed two:
> >> >>> > A) create a wrapper class for legacy Stream compatibility
> selectors
> >> >>> > B) create extensions for Legacy Stream compatibility selectors
> >> >>> > My preference goes to A)
> >> >>>
> >> >>> By wrappers you mean the Xtreams are the innards doing the work and
> >> >>> the wrappers providing the legacy API?
> >> >>>
> >> >>> This would be a great way to test Xtreams.
> >> >>>
> >> >>> > The legacy support MUST be minimal (next nextPut: nextPutAll: peek
> >> >>> > upTo:
> >> >>> > ...), otherwise we will import all the cruft in Xtream and would
> go
> >> >>> > back
> >> >>> > to
> >> >>> > our starting point...
> >> >>> > Once the minimal support written (a few hours should be enough),
> we
> >> >>> > should
> >> >>> > gradually switch each every legacy Stream usage -> Xtream.
> >> >>> >
> >> >>> > An area which require more work is those Streams that have mixed
> >> >>> > conventions
> >> >>> > (one portion is interpreted as text, another as binary).
> >> >>> > In theory that's easy, we just have two streams and they both wrap
> >> >>> > on a
> >> >>> > low
> >> >>> > level binary stream, but that means we have to be very cautious
> with
> >> >>> > buffers
> >> >>> > and caches.
> >> >>> >
> >> >>> > Another area of work is usage of ugly selectors like name (we try
> to
> >> >>> > access
> >> >>> > the file name from the Stream API, arghh). Those usages are bad
> and
> >> >>> > require
> >> >>> > a rewrite.
> >> >>>
> >> >>> Are you saying a FileStream knowing its #name or #filename is bad?
> >> >>>
> >> >>
> >> >
> >>
> >
>
>
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