Dereference Hash of Hash

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

Hi,

I would like to dereference a Hash of Hash within a string.

Normally I do it like this

print "MyText${var}ishere";
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How can I use the brackets when dereferecing a Hash of hash?

This does not work:

print "MyText${ref_HoH}->{$var}->{key}ishere."

print "MyText${ref_HoH->{$var}->{key}}ishere."

This works but I think this not a very good way ...

print "MyText$ref_HoH->{$var}->{key}ishere."
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Thanks for help.

regards de Michi

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Re: Dereference Hash of Hash - print
by LanX (Saint) on Oct 12, 2014 at 21:13 UTC

> This works but I think this not a very good way ...

It is, but you can avoid one arrow

print "MyText$ref_HoH->{$var}{key}ishere."

You can also try (untested)

print "MyText$$ref_HoH{$var}{key}ishere."

Anyway I'd prefer something more readable, so why interpolating?

update

This looks like an XY problem, do you really need 2 levels?

Cheers Rolf

_{(addicted to the Perl Programming Language and ☆☆☆☆ :)}

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Re: Dereference Hash of Hash - print
by Athanasius (Archbishop) on Oct 13, 2014 at 03:10 UTC

Hello demichi,

I agree with LanX, readability is the key here. Consider the following, which all print MyTextWilmaishere.:

#! perl
use strict;
use warnings;

my $ref_HoH =
{
    Fred   => { wife => 'Wilma', daughter => 'Pebbles',   },
    Barney => { wife => 'Betty', son      => 'Bamm-Bamm', },
};

my $var = 'Fred';
my $key = 'wife';

print  "MyText$ref_HoH->{$var}{$key}ishere.\n";             # interpol
+ated
print  "MyText$$ref_HoH{$var}{$key}ishere.\n";              # interpol
+ated
print  "MyText" . $ref_HoH->{$var}{$key} . "ishere.\n";     # concaten
+ated
print  "MyText" . $$ref_HoH{$var}{$key} . "ishere.\n";      # concaten
+ated
printf "MyText%sishere.\n", $ref_HoH->{$var}{$key};         # template
+d
printf "MyText%sishere.\n", $$ref_HoH{$var}{$key};          # template
+d
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My preference is for printf, which presents the complete structure of the output up-front, in the format string; but concatenation is always a valid option; and either option is clearer, and therefore more maintainable, than the equivalent interpolation.

Hope that helps,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

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