Is this a hash?

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

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Re: Is this a hash? by toolic (Bishop) on Jun 16, 2015 at 14:29 UTC
$thing is a scalar variable which contains a reference to a hash (defined with the curlies). See perlreftut and perldata. This shows a hash variable (using parentheses): `my %thing = ( a => $a, b => $b, );` [download]	[reply] [d/l]
Re: Is this a hash? by davido (Cardinal) on Jun 16, 2015 at 14:29 UTC
`$thing` will contain a hash reference, or more precisely, a reference to an anonymous hash constructed by the `{ ... }` operator, which in this usage is a hash reference constructor. You can refer to the hash as a reference (`$thing`), or as a hash (`%{$thing}` or `%$thing`), and you may refer to its individual elements by dereferencing it: `$thing->{'a'}`. This would be a named hash: `my %thing = ( a => $a, b => $b, );` [download] Dave	[reply] [d/l] [select]
Re: Is this a hash? by pme (Monsignor) on Jun 16, 2015 at 14:32 UTC
Hi nhnl, Welcome to the monastery! $thing is a hashref. You can read more about perlrefs perlref and perlreftut. `use strict; use Data::Dumper; my $a = 5; my $b = 6; my $thing = { a => $a, b => $b, }; print Dumper($thing) . "\n";` [download] output is `$VAR1 = { 'a' => 5, 'b' => 6 };` [download]	[reply] [d/l] [select]
Re: Is this a hash? by talexb (Chancellor) on Jun 16, 2015 at 18:16 UTC
You've got a pile of answers already, but here's one more! Here's a hash: `my %hash = ( a => 1, b => 2 ); print $hash{'b'}; # prints 2` [download] And here's a hashref, which is like the one that you had: `my $hashref = { c => 3, d => 4 }; print $hashref->{c}; # prints 3` [download] As you can see, you use percent and brackets to define a hash, and dollar and braces to define a hashref. In addition, you can get a reference to something by putting a backslash in front of it .. `my $ref_to_hash = \%hash; print $ref_to_hash->{'a'}; # prints 1` [download] References are useful when you want to pass data structures around -- it's more efficient to pass a reference (that big thing over there) rather than the structure itself. Alex / talexb / Toronto Thanks PJ. We owe you so much. Groklaw -- RIP -- 2003 to 2013.	[reply] [d/l] [select]