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Message from discussion PerlHash using PMCs for keys?
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Leopold Toetsch  
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 More options Jun 4 2004, 4:58 am
Newsgroups: perl.perl6.internals
From: l...@toetsch.at (Leopold Toetsch)
Date: Fri, 4 Jun 2004 10:58:51 +0200
Local: Fri, Jun 4 2004 4:58 am
Subject: Re: PerlHash using PMCs for keys?
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Piers Cawley <pdcaw...@bofh.org.uk> wrote:
> Leopold Toetsch <l...@toetsch.at> writes:
>> Just use a Key PMC for $P2.
> So, just for fun I added the following test to t/pmc/perlhash.t:
>     new P10, .PerlHash
>     new P1, .PerlString
>     set P1, "Bar"
>     new P2, .Key
>     set P2, P1

      ^^^

C<set Px, Py> aliases the two PMCs, both are pointing to the same PMC
then. You'd like to use C<assign> here.

>     new P3, .Key
>     set P2, P1

          ^^
typo?

> Perl 6 supports using full on objects as keys in its hashes. It seems
> that having parrot do the same would be a Good Thing.

The main problem here is, what does ...

  set P0, P1[P2]

... mean: keyed_string or keyed_integer, i.e. hash or array lookup.
The Key PMC provides this information, a plain string could be used in
both ways:

  set P2, "42"
  set P0, P1[P2]

It depends of course on the aggregate, what kind of key it would like to
use, but e.g. for an OrderedHash PMC, which supports lookup by string
*and* by integer, the usage is ambiguous.

We could change C<key.c:key_integer()> to extract a number with
C<get_integer> from any PMC and do the same with C<key_string> but some
keyed usage needs a defined type.

leo


 
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