http://www.perlmonks.org?node_id=904238

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

Wait a minute --- what's wrong with these lines ?! These look perfectly fine!

$WAI is an object, which I call getMem() which returns a hashref, I then address a piece of the hashref with ->{'MemTotal'} and take that inside the object's converter function kBToMB().

Is this bad ?? What's a better way to achieve the same thing?

----------------------------

sub get_memory_tot {
        return $WAI->kBToMB( %{$WAI->getMem()}->{'MemTotal'} );
}

sub get_memory_free {
        return $WAI->kBToMB( %{$WAI->getMem()}->{'MemFree'} );
}

sub get_swap {
        return $WAI->kBToMB( %{ $WAI->getMem() }->{'SwapTotal'});
}

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Replies are listed 'Best First'.
Re: "Using a hash as a reference is deprecated" -- Baloney !
by kennethk (Abbot) on May 11, 2011 at 20:15 UTC
    If getMem() is returning a hash reference, then you are dereferencing the hashref into a hash with %{ ... } and then dereferencing a second time using The Arrow Operator, thus the warning. The preferred syntax would be: 

    sub get_memory_tot {
        return $WAI->kBToMB($WAI->getMem()->{'MemTotal'} );
}

sub get_memory_free {
        return $WAI->kBToMB( $WAI->getMem()->{'MemFree'} );
}

sub get_swap {
        return $WAI->kBToMB( $WAI->getMem()->{'SwapTotal'});
}

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    See perlref and/or perlreftut for more explanation.

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Re: "Using a hash as a reference is deprecated" -- Baloney !
by NetWallah (Canon) on May 11, 2011 at 20:17 UTC
    Paraphrasing from from perlop:The left side of the "->" ( infix dereference operator) must be a REFERENCE to ....

    In your case, you are supplying a HASH (Not a reference).

    Just get rid of the %{...} , and you will have a (Hash) reference. 

                 return $WAI->kBToMB( $WAI->getMem()->{MemTotal} );

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    (No need for quotes inside {} ).

         Syntactic sugar causes cancer of the semicolon.        --Alan Perlis

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Re: "Using a hash as a reference is deprecated" -- Baloney !
by ikegami (Patriarch) on May 11, 2011 at 20:24 UTC

    Due to a bug in Perl, 

    %foo->{bar}

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    gets interpreted as a 

    (\%foo)->{bar}

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    ->{bar} expects a reference, and thus a scalar, so it should be interpreted as 

    scalar(%foo)->{bar}

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    The deprecation warning was added in anticipation of getting this bug fixed.

    Since 

    %{$WAI->getMem()}->{'MemTotal'}

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    is getting interpreted as 

    \%{$WAI->getMem()}->{'MemTotal'}

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    you could use that, or you could shorten it to 

    $WAI->getMem()->{'MemTotal'}

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    Now where's this baloney you promised? I'm hungry!

    Update: Fixed bad curlies matching in second half.

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      Awesome. Excellent explanation, I had no idea this was a planned bugfix. Thanks everyone ! Here's the promised "baloney" :) 
      Balogna ("baloney") and cheese:


                    _.---._
                _.-~       ~-._
            _.-~               ~-._
        _.-~                       ~---._
    _.-~                                 ~\
 .-~                                    _.;
 :-._                               _.-~./
 }-._~-._                   _..__.-~_.-~ )
 `-._~-._~-._              /   ...-~H.-~
     ~-nad.._\.        _.-~ .::::  //
         ~-. \`--...--~ _.-~__...==~
            \.`--...---+-~~~~~
              ~-..----~

How about a deli style turkey sandwich (damn I'm hungry now!):

                    _.---._
                _.-~       ~-._
            _.-~               ~-._
        _.-~                       ~---._
    _.-~                                 ~\
 .-~                                    _.;
 :-._                               _.-~ ./
 `-._~-._                   _..__.-~ _.-~
  /  ~-._~-._              / .__..--~----._
 \_____(_;-._\.        _.-~_/       ~).. . \
    /(_____  \`--...--~_.-~______..-+_______)
  .(_________/`--...--~/    _/nad        /\
 /-._     \_     (___./_..-~__.....__..-~./
 `-._~-._   ~\--------~  .-~_..__.-~ _.-~
     ~-._~-._ ~---------'  / .__..--~
         ~-._\.        _.-~_/
             \`--...--~_.-~
              `--...--~


Gotta have something to wash that down with...

                                                           _
                                                          //
                                                         //
                                         _______________//__
                                       .(______________//___).
                                       |              /      |
                                       |. . . . . . . / . . .|
                                       \ . . . . . ./. . . . /
                                        |           / ___   |
                    _.---._             |::......./../...\.:|
                _.-~       ~-._         |::::/::\::/:\::::::|
            _.-~               ~-._     |::::\::/::::::X:/::|
        _.-~                       ~---.;:::::::/::\::/:::::|
    _.-~                                 ~\::::::n::::::::::|
 .-~                                    _.;::/::::a::::::::/
 :-._                               _.-~ ./::::::::d:::::::|
 `-._~-._                   _..__.-~ _.-~|::/::::::::::::::|
  /  ~-._~-._              / .__..--~----.YWWWWWWWWWWWWWWWP'
 \_____(_;-._\.        _.-~_/       ~).. . \
    /(_____  \`--...--~_.-~______..-+_______)
  .(_________/`--...--~/    _/           /\
 /-._     \_     (___./_..-~__.....__..-~./
 `-._~-._   ~\--------~  .-~_..__.-~ _.-~
     ~-._~-._ ~---------'  / .__..--~
         ~-._\.        _.-~_/
             \`--...--~_.-~
              `--...--~

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      credit to : Nate / DAC for the artwork !

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Re: "Using a hash as a reference is deprecated" -- Baloney !
by LanX (Saint) on May 11, 2011 at 20:23 UTC
    Well you are overcompensating! ;)

    Either $WAI->getMem()->{'SwapTotal'} or (which nobody mentioned yet)  %{ $WAI->getMem() }{'SwapTotal'} but not both.

    Old perl versions allowed to write %hash->{key} but as you see it's deprecated now.

    Cheers Rolf

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