PERL Miscellaneous

Author

tied hash

Konrad Eisele

2005-07-27, 5:05 pm

I have a tied hash, say %a. On a tied 'STORE' I want to get the return
values of the STORE function. is that possible? a naive aproach would be
@a = ($a{'key'} = 'value'); however this returns still the tied FETCH
of $a{'key'}. How do i have to reorder the expression??

-- Konrad

%a = ();
tie %a,'Ta';
@a = ($a{'key'} = 'value');

package Ta;
use Tie::Hash;
@ISA = qw(Tie::StdHash);

sub STORE {
return [1,2,3];
}

I'd like to get @a == [1,2,3]

Paul Lalli

2005-07-27, 5:05 pm

Konrad Eisele wrote:
> I have a tied hash, say %a. On a tied 'STORE' I want to get the return
> values of the STORE function. is that possible? a naive aproach would be
> @a = ($a{'key'} = 'value'); however this returns still the tied FETCH
> of $a{'key'}. How do i have to reorder the expression??
>
> -- Konrad
>
> %a = ();
> tie %a,'Ta';
> @a = ($a{'key'} = 'value');
>
>
> package Ta;
> use Tie::Hash;
> @ISA = qw(Tie::StdHash);
>
> sub STORE {
> return [1,2,3];
> }
>
> I'd like to get @a == [1,2,3]

>From perldoc perltie:
Don't worry about returning a value from STORE -- the semantic of
assignment returning the assigned value is implemented with FETCH

It sounds to me like what you're asking for isn't possible. Assignment
is defined to return the value of FETCH'ing, not STORE'ing.

It might be a good idea at this point to ask yourself why you feel the
need to do this in the first place. Perhaps if you tell us what your
end goal is, someone can suggest a better method than attempting to
return a value from STORE()

Paul Lalli

attn.steven.kuo@gmail.com

2005-07-27, 5:05 pm

Konrad Eisele wrote:
> I have a tied hash, say %a. On a tied 'STORE' I want to get the return
> values of the STORE function. is that possible? a naive aproach would be
> @a = ($a{'key'} = 'value'); however this returns still the tied FETCH
> of $a{'key'}. How do i have to reorder the expression??
>
> -- Konrad
>
>
>
>
> %a = ();
> tie %a,'Ta';
> @a = ($a{'key'} = 'value');
>
>
> package Ta;
> use Tie::Hash;
> @ISA = qw(Tie::StdHash);
>
> sub STORE {
> return [1,2,3];
> }
>
>
>
>
> I'd like to get @a == [1,2,3]

Couldn't you avoid the STORE operation entirely
and assign to @a first? If you want it on
one line, then try something like:

tie %foo, 'Ta';
$foo{bar} = [ my @a = ([1, 2, 3]) ]->[0];

--
Hope this helps,
Steven

Anno Siegel

2005-07-28, 9:09 am

Konrad Eisele <konrad@gaisler.com> wrote in comp.lang.perl.misc:
> I have a tied hash, say %a. On a tied 'STORE' I want to get the return
> values of the STORE function. is that possible? a naive aproach would be
> @a = ($a{'key'} = 'value'); however this returns still the tied FETCH
> of $a{'key'}. How do i have to reorder the expression??
>
> -- Konrad
>
>
>
>
> %a = ();
> tie %a,'Ta';
> @a = ($a{'key'} = 'value');

When this happens, @Ta::ISA is not yet set.

> package Ta;
> use Tie::Hash;
> @ISA = qw(Tie::StdHash);

This happens too late. Wrap "BEGIN {}" around it.

> sub STORE {
> return [1,2,3];
> }

Your example program doesn't use your STORE method.

But even if it did, what is returned by an assignment is always the
variable on the left hand side (with the new value already in it).
If that happens to be tied, or, in your example, happens to be a value
in a tied hash, that doesn't change that fact. The value you see will
be the value stored (as read back by READ), no matter what STORE returns.

Anno
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