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### Mini-Tutorial: Dereferencing Syntax

by ikegami (Pope)
 on Jun 20, 2012 at 16:54 UTC Need Help??

Direct Using References
Syntax 1[1] Syntax 2
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]
1. The curly brackets around \$sr, \$ar, \$hr, \$cr and \$gr are optional when the contents of the curlies is simply a scalar.
2. Requires Perl 5.20+.
3. Requires Perl 5.24+. Available in Perl 5.20+ by adding both use feature qw( postderef ); and no warnings qw( experimental::postderef );.

Replies are listed 'Best First'.
Re: Mini-Tutorial: Dereferencing Syntax
by tobyink (Abbot) 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'}

The first one is basically a shorthand for:

```(\$hash{'key1'}, \$hash{'key2'})

The second one is:

```\$hash{join(\$;, 'key1', 'key2')}

... 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'

And similarly (though not identically, certainly) for arrays.

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.
Re: Mini-Tutorial: Dereferencing Syntax
by Anonymous Monk on Jun 21, 2012 at 13:06 UTC
Not mentioned:   \$\$foo as shorthand for \$foo->.

\$\$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.

You're probably thinking of the equivalency of \$\$foo[...] and \$foo->[...] and of \$\$foo{...} and \$foo->{...}, but that's already mentioned.

Re: Mini-Tutorial: Dereferencing Syntax
by ikegami (Pope) 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.

Re: Mini-Tutorial: Dereferencing Syntax
by DrHyde (Prior) on Nov 25, 2013 at 11:31 UTC
Huzzah for the slice syntax!

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