Mini-Tutorial: Dereferencing Syntax

Whenever you can use the name of a variable, you can use a block that evaluates to a reference instead. For example, the following are valid syntax for specifying an array:

@NAME    # If you have the name      e.g. @array
@BLOCK   # If you have a reference   e.g. @{ $ref }
[download]

This is the "circumfix syntax" illustrated in the table below.

An alternative syntax colloquially known as the "arrow notation" is easier to read, but requires Perl 5.20+ in some cases. This is the "postfix syntax" illustrated in the table below.

Direct Using References
Circumfix Syntax^[1] Postfix Syntax
scalar itself $s ${$sr} $sr->$*^[3]
array itself @a @{$ar} $ar->@*^[3]
element $a[0] ${$ar}[0] $ar->[0]
slice @a[0,1,2] @{$ar}[0,1,2] $ar->@[0,1,2]^[3]
index/value slice^[2] %a[0,1,2] %{$ar}[0,1,2] $ar->%[0,1,2]^[3]
last index $#a $#{$ar} $ar->$#*^[3]
hash itself %h %{$hr} $hr->%*^[3]
element $h{'a'} ${$hr}{'a'} $hr->{'a'}
slice @h{'a','b','c'} @{$hr}{'a','b','c'} $hr->@{'a','b','c'}^[3]
key/value slice^[2] %h{'a','b','c'} %{$hr}{'a','b','c'} $hr->%{'a','b','c'}^[3]
code call func(@args)
call (prototype ignored) &func(@args) &{$cr}(@args) $cr->(@args)
call (inherited @_) &func &{$cr} $cr->&*^[3]
glob itself *glob *{$gr} $gr->**^[3]
slot *glob{ARRAY} *{$gr}{ARRAY} $gr->*{ARRAY}^[3]

The curly brackets around $sr, $ar, $hr, $cr and $gr are optional when the contents of the curlies is simply a scalar.
Requires Perl 5.20+.
Requires Perl 5.24+. Available in Perl 5.20+ by adding both use feature qw( postderef ); and no warnings qw( experimental::postderef );, or by adding use experimental qw( postderef );. This is safe because the then-experimental feature was accepted into Perl without change.

See also:

Comment on Mini-Tutorial: Dereferencing Syntax Select or Download Code

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Re: Mini-Tutorial: Dereferencing Syntax by tobyink (Canon) on Jun 20, 2012 at 19:50 UTC
It's also worth noting that the following are two completely different things. `@hash{'key1', 'key2'} $hash{'key1', 'key2'}` [download] The first one is basically a shorthand for: `($hash{'key1'}, $hash{'key2'})` [download] The second one is: `$hash{join($;, 'key1', 'key2')}` [download] ... where `$;` is the subscript separator, which defaults to \034. `perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'`	[reply] [d/l] [select]
Re^2: Mini-Tutorial: Dereferencing Syntax by jdporter (Paladin) on Jun 20, 2012 at 21:51 UTC
And similarly (though not identically, certainly) for arrays.	[reply]
Re^2: Mini-Tutorial: Dereferencing Syntax by ikegami (Patriarch) on Sep 17, 2012 at 05:36 UTC
The difference between hash lookups and hash slices has nothing to do with references or how to use them. I shall not add such a note.	[reply]
Re: Mini-Tutorial: Dereferencing Syntax by ikegami (Patriarch) on Nov 22, 2013 at 21:53 UTC
Updated for Perl 5.20. ...And previously missing `$ar->$#*` was added to both Perl and this document.	[reply] [d/l]
Re^2: Mini-Tutorial: Dereferencing Syntax by Anonymous Monk on Nov 23, 2013 at 07:56 UTC
https://metacpan.org/pod/release/BINGOS/perl-5.19.6/pod/perlref.pod#Postfix-Dereference-Syntax	[reply]
Re: Mini-Tutorial: Dereferencing Syntax by Anonymous Monk on Jun 21, 2012 at 13:06 UTC
Not mentioned: `$$foo` as shorthand for `$foo->`.	[reply]
Re^2: Mini-Tutorial: Dereferencing Syntax by ikegami (Patriarch) on Sep 17, 2012 at 05:03 UTC
`$$foo` is not a shorthand for `$foo->`. `>perl -E"$foo=\'foo'; say $$foo;" foo >perl -E"$foo=\'foo'; say $foo->;" syntax error at -e line 1, near "->;" Execution of -e aborted due to compilation errors.` [download] You're probably thinking of the equivalency of `$$foo[...]` and `$foo->[...]` and of `$$foo{...}` and `$foo->{...}`, but that's already mentioned.	[reply] [d/l] [select]
Re: Mini-Tutorial: Dereferencing Syntax by DrHyde (Prior) on Nov 25, 2013 at 11:31 UTC
Huzzah for the slice syntax!	[reply]


go ahead... be a heretic
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