drone has asked for the wisdom of the Perl Monks concerning the following question:

Greetings all. I have a coworker here that insists on accessing hash values like this:
$value = %hash->{key};

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This apparently works but I have never seen something like that in the manuals or Perl books.
To test things out I tried this:
@array = ('a','b','c');
print @array->[2], "\n";

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This works too and it seems to me that %hash and @array behave like references to themselves.

Would some wise monk care to shed some light on this?

Thanks!

Replies are listed 'Best First'.
Re: Unusual way of accessing hash values
by gaal (Parson) on May 05, 2005 at 12:04 UTC
    From perldiag: 

    Using a hash as a reference is deprecated
    (D deprecated) You tried to use a hash as a reference, as in
    "%foo->{"bar"}" or "%$ref->{"hello"}". Versions of perl <= 5.6.1
    used to allow this syntax, but shouldn’t have. It is now deprecate
+d,
    and will be removed in a future version.

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Re: Unusual way of accessing hash values
by gellyfish (Monsignor) on May 05, 2005 at 12:05 UTC

    In the hash example you would get: 

    Using a hash as a reference is deprecated at ....

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    in the array example you would get: 
    Using an array as a reference is deprecated at ...

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    if you had use warnings (or -w).

    /J\

    :
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Re: Unusual way of accessing hash values
by polettix (Vicar) on May 05, 2005 at 12:42 UTC
    This seems to apply to function calls as well. As seen in holli's homenode, from the CB:
    diotalevi Huh. Foo->() is merely alternative syntax for Foo(). I never knew that.
    jZed a man walks into a Bar->(), bartender says, did you know that arrow is redundant?

    Flavio (perl -e 'print(scalar(reverse("\nti.xittelop\@oivalf")))')

    Don't fool yourself.
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Re: Unusual way of accessing hash values
by drone (Monk) on May 05, 2005 at 12:13 UTC
    Thanks gaal and gellyfish! Didn't even know there was a perldiag :)
    And of course using warnings would save me a lot of trouble in explaining some facts to my coworker!
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      One other reason I sometimes temporarily turn on diagnostics is to find out what keyword to use when I want to selectively turn off a particular group of warnings. For example, in this case yo see that the body of the diagnostic message begins with (D deprecated). If for some reason I wanted to turn off such warnings in a suitably narrowed scope, I would do this: 

      use strict;
use warnings;
# ...
{
  no warnings 'deprecated';
  %hash->{ silly } = 'foo';
}

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      Granted, I can't think of any good reason for turning off this particular warning (except perhaps globally on a large body of legacy code), but there are more realistic examples. E.g.: 
      use strict;
use warnings;
require Exporter;
{
  no warnings 'once';
  *import = \&Exporter::import;
}

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      The no warnings above silences a warning of the form 
      Name "main::import" used only once: possible typo...

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      Yes, one could silence this warning like this instead: 

      *import = *import = \&Exporter::import;

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      ...but I digress.

      the lowliest monk

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      If you're ever unsure as to what a warning means, you can ... 
      use diagnostics;

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      which would print the exact text as posted in the the first reply.
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        Or pipe the error messages through the splain program.

        Man, it'd be great if the cow-orker in question was named "Lucy". Lucy, joo gots some splain'in to do!

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