Classlib: Add 'rewind' to CollStream

[jamshark70]

I've been using CollStream as part of a parser, and it's very useful to roll back 1 or more characters.

Currently:

stream.pos = stream.pos - 1;

Proposed:

stream.rewind(1);

No rush on this.

(CollStream is as yet undocumented, btw.)

[telephon]

If you provide no argument, stream.rewind, sounds like "fully rewind". Couldn't the default be that?

rewind { |n|
if(n.isNil) { pos = 0 } {
        pos = max(0, pos - n)
}
}

[jamshark70]

I see your point. That would mean rewind with no argument would be a synonym for reset -- using it as a synonym may or may not be desirable. Don't know. When I used it as a private extension, I always gave the argument (to be explicit, consistent and readable) so I wouldn't object this change.

[telephon]

whatever you prefer, either way is fine!

in this way it probably would be:

rewind { |n|
if(n.isNil) { 
       this.reset
 } {
        pos = max(0, pos - n)
}
}

[telephon]

any opinions on that? I'm fine either way.

[telephon]

I'd like to merge it as it is now, if there are no objections.

[mossheim]

There's an opportunity here to copy the interface from File. If we rework the method as seek, rewind(n) becomes seek(-n, 1), and it also gives us access to end-of-stream offsets seek(0, 2). For some reason the documentation for UnixFILE says this is what pos does, but I don't think that's accurate as the class doesn't actually define that method and its immediate superclass implements it as subclassResponsibility.

[telephon]

I think, because seek is a little "special", with its numerical behavior switch, we should have both. @brianlheim is it that what you meant?

[mossheim]

I would be OK with both so long as it introduces consistency between File and CollStream etc. This is not so "special" IMO since it is also found in C and Python, just historically motivated. FWIW C/C++ has std::rewind which without an argument returns to the beginning of the stream. That would make more sense to me as a default argument as well. But I'm fine either way, as @jamshark70 pointed out you usually want to move back by one.

[telephon]

good! (I meant "special" relative to the semantic style elsewhere in sclang, where behaviour is normally not numbered but named, doneAction notwithstanding …)

[mossheim]

Ah, ok :)

[telephon]

I'll do the seek implementation in a separate PR.