Thanks Rob, this has been very helpful. I wanted to know why the second
form is an abuse of perl. Since I'm new to perl, it is helpful to kn ow
what is good programming practise.
Tx.
H
On Tue, 2003-06-10 at 15:39, Rob Dixon wrote:
> Hamish Whittal wrote:
> > Hi All,
> >
> > I'm still a little confused...
> > What is the difference between
> > %{$config_file->{$key}}
>
> Here, $config_file is a hash reference. If you print it it will
> display something like
>
> HASH(0x12345678)
>
> The hash it refers to is accessed by the value in $key, so if
> you had
>
> my $config_file = { K => { K2 => 'V2' } };
> my $key = 'K';
>
> then
>
> $config_file->{$key}
>
> would be equal to the anonymous hash { K2 => 'V2' }.
>
> This value is then dereferenced again as a hash, so if
> we have
>
> my %hash = %{$config_file->{$key}};
>
> then
>
> $config_file->{$key}
>
> %hash would be set to
>
> %hash = ( K2 => V2 );
>
>
>
> > %$config_file->{$key}
>
> Now this is something altogether different. You've
> discovered that you can use hash names as references,
> and this is an abuse of Perl and not to be encouraged!
>
> If you had
>
> my %config = ( K => { K1 => 'V1' } );
> my $config_file = \%config;
>
> then %$config_file is the same as %config, so you can access
> the element with
>
> $config{K}
> or
> $config_file->{K}
>
> What the book doesn't tell you, though, is that Perl will
> let you treat the hash name as a reference like this
>
> %config->{K}
>
> which is the same as
>
> %$config_file->{K}
>
> So you've dereferenced $config_file and then used it as a reference,
> so achieving nothing.
>
> To summarize:
>
> %$config_file->{$key}
>
> is the same as
>
> $config_file->{$key}
>
> and so is the same as the first case, %{$config_file->{$key}}
> without the additional level of dereferencing.
>
> But, as I said, don't use the second case!
>
> Cheers,
>
> Rob
>
>
--
You are not defined by what loves you, but what you love - Nicholas Cage
(Adaptation, 2003)
---
Hamish Whittal
QED Technologies cc
+27 82 803 5533
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