Re: (random) musings on I/O disciplines

At 07:20 PM 9/27/00 +0100, Nicholas Clark wrote:
>On Wed, Sep 27, 2000 at 01:26:18PM -0400, Dan Sugalski wrote:
> > At 11:04 PM 9/26/00 +0100, Simon Cozens wrote:
> > >Well, let's go over here, then. I just submitted an RFC for internal 
> string
> > >abstraction, which may or may not be the same thing as what you were just
> > >talking about.
> >
> > Well, the impression I get from Larry is that he wants the internals to be
> > character-formatting neutral. Scalars should be able to provide their
> > contents in a number of different formats, but perl would usually not have
> > One True Format internally. (Though how many True Formats there were might
> > depend on the size of the platform--tiny ones might be all Unicode, or
> > ASCII, or something)
> >
> > I think the intention is that if data comes in in ASCII or EBCDIC or
> > Unicode or Shift-JIS or binary or whatever then perl will keep it that way
> > if it understands the format, and convert as needed by bits of the core.
>
>Which to me would suggest that there would be an API whereby code would
>ask "can I have the contents of this SV in format blah" (where blah was one
>of the core's understood formats) and you'd get data either direct from the
>(son of) SV, or trigger a conversion from whatever format the SV actually
>held data in.

Yup, that's built into the vtable stuff. There's a 'get_string' entry in 
the vtable that is really an array of function pointers. Each entry in the 
array returns the scalar's data in a different format. Entry 0 returns raw 
bytes, 1 might be UTF8, 2 UTF16, 3 EBCDIC, 4 UTF32, 4 Shift-JIS... you get 
the picture.

Conversion might be lossy (EBCDIC<->ASCII generally is) and might go 
through several steps if a variable doesn't know how to get from A to B 
(EBCDIC to Shift-JIS, say), but that's OK.

>And all parts of perl would only get data via that API (ie all files not
>called sv.c for current perl on a strict interpretation)
>
>Whether that conversion was cached (And how long for) would be left as
>an exercise for the garbage collector.

Or the variable itself. Integers might not cache their conversion to 
strings, for example.

I really need to finish the vtable RFC and get it into -internals for 
another going over.

					Dan

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Dan Sugalski                          even samurai
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