a list of references!
@list = (\$a, \@b, \%c);
- @list = \($a, @b, %c); # same thing!
+ @list = \($a, @b, %c); # same thing!
As a special case, C<\(@foo)> returns a list of references to the contents
of C<@foo>, not a reference to C<@foo> itself. Likewise for C<%foo>,
brackets:
$hashref = {
- 'Adam' => 'Eve',
- 'Clyde' => 'Bonnie',
+ 'Adam' => 'Eve',
+ 'Clyde' => 'Bonnie',
};
Anonymous hash and array composers like these can be intermixed freely to
closures work:
sub newprint {
- my $x = shift;
- return sub { my $y = shift; print "$x, $y!\n"; };
+ my $x = shift;
+ return sub { my $y = shift; print "$x, $y!\n"; };
}
$h = newprint("Howdy");
$g = newprint("Greetings");
(L<perlfunc/socket> and L<perlfunc/socketpair>), and directory
handles (L<perlfunc/opendir>). For compatibility with previous
versions of Perl, C<*foo{FILEHANDLE}> is a synonym for C<*foo{IO}>, though it
-is deprecated as of 5.8.0. If deprecation warnings are in effect, it will warn
-of its use.
+is discouraged, to encourage a consistent use of one name: IO. On perls
+between v5.8 and v5.22, it will issue a deprecation warning, but this
+deprecation has since been rescinded.
C<*foo{THING}> returns undef if that particular THING hasn't been used yet,
except in the case of scalars. C<*foo{SCALAR}> returns a reference to an
value to a scalar instead of a typeglob as we do in the examples
below, there's no risk of that happening.
- splutter(*STDOUT); # pass the whole glob
- splutter(*STDOUT{IO}); # pass both file and dir handles
+ splutter(*STDOUT); # pass the whole glob
+ splutter(*STDOUT{IO}); # pass both file and dir handles
sub splutter {
- my $fh = shift;
- print $fh "her um well a hmmm\n";
+ my $fh = shift;
+ print $fh "her um well a hmmm\n";
}
- $rec = get_rec(*STDIN); # pass the whole glob
+ $rec = get_rec(*STDIN); # pass the whole glob
$rec = get_rec(*STDIN{IO}); # pass both file and dir handles
sub get_rec {
- my $fh = shift;
- return scalar <$fh>;
+ my $fh = shift;
+ return scalar <$fh>;
}
=back
the BLOCK can contain any arbitrary expression, in particular,
subscripted expressions:
- &{ $dispatch{$index} }(1,2,3); # call correct routine
+ &{ $dispatch{$index} }(1,2,3); # call correct routine
Because of being able to omit the curlies for the simple case of C<$$x>,
people often make the mistake of viewing the dereferencing symbols as
Consider the difference below; case 0 is a short-hand version of case 1,
I<not> case 2:
- $$hashref{"KEY"} = "VALUE"; # CASE 0
- ${$hashref}{"KEY"} = "VALUE"; # CASE 1
- ${$hashref{"KEY"}} = "VALUE"; # CASE 2
- ${$hashref->{"KEY"}} = "VALUE"; # CASE 3
+ $$hashref{"KEY"} = "VALUE"; # CASE 0
+ ${$hashref}{"KEY"} = "VALUE"; # CASE 1
+ ${$hashref{"KEY"}} = "VALUE"; # CASE 2
+ ${$hashref->{"KEY"}} = "VALUE"; # CASE 3
Case 2 is also deceptive in that you're accessing a variable
called %hashref, not dereferencing through $hashref to the hash
X<reference, numeric context>
if ($ref1 == $ref2) { # cheap numeric compare of references
- print "refs 1 and 2 refer to the same thing\n";
+ print "refs 1 and 2 refer to the same thing\n";
}
Using a reference as a string produces both its referent's type,
People frequently expect it to work like this. So it does.
$name = "foo";
- $$name = 1; # Sets $foo
- ${$name} = 2; # Sets $foo
- ${$name x 2} = 3; # Sets $foofoo
- $name->[0] = 4; # Sets $foo[0]
- @$name = (); # Clears @foo
- &$name(); # Calls &foo()
+ $$name = 1; # Sets $foo
+ ${$name} = 2; # Sets $foo
+ ${$name x 2} = 3; # Sets $foofoo
+ $name->[0] = 4; # Sets $foo[0]
+ @$name = (); # Clears @foo
+ &$name(); # Calls &foo()
$pack = "THAT";
- ${"${pack}::$name"} = 5; # Sets $THAT::foo without eval
+ ${"${pack}::$name"} = 5; # Sets $THAT::foo without eval
This is powerful, and slightly dangerous, in that it's possible
to intend (with the utmost sincerity) to use a hard reference, and
local $value = 10;
$ref = "value";
{
- my $value = 20;
- print $$ref;
+ my $value = 20;
+ print $$ref;
}
This will still print 10, not 20. Remember that local() affects package
using strict refs:
use strict 'refs';
- ${ bareword }; # Okay, means $bareword.
- ${ "bareword" }; # Error, symbolic reference.
+ ${ bareword }; # Okay, means $bareword.
+ ${ "bareword" }; # Error, symbolic reference.
Similarly, because of all the subscripting that is done using single words,
the same rule applies to any bareword that is used for subscripting a hash.
@colors = qw(red blue green yellow orange purple violet);
for my $name (@colors) {
- no strict 'refs'; # allow symbol table manipulation
+ no strict 'refs'; # allow symbol table manipulation
*$name = *{uc $name} = sub { "<FONT COLOR='$name'>@_</FONT>" };
}
$r = [ 1, [ 2, 3 ], 4 ];
$r->[1]->@*; # equivalent to @{ $r->[1] }
-This syntax must be enabled with C<use feature 'postderef'>. It is
-experimental, and will warn by default unless C<no warnings
-'experimental::postderef'> is in effect.
+In Perl 5.20 and 5.22, this syntax must be enabled with C<use feature
+'postderef'>. As of Perl 5.24, no feature declarations are required to make
+it available.
Postfix dereference should work in all circumstances where block
(circumfix) dereference worked, and should be entirely equivalent. This
Postfix array and scalar dereferencing I<can> be used in interpolating
strings (double quotes or the C<qq> operator), but only if the
-
additional C<postderef_qq> feature is enabled.
+C<postderef_qq> feature is enabled.
=head2 Postfix Reference Slicing
As with postfix array, postfix value slice dereferencing I<can> be used
in interpolating strings (double quotes or the C<qq> operator), but only
-if the
additional C<postderef_qq> L<feature> is enabled.
+if the C<postderef_qq> L<feature> is enabled.
=head1 Assigning to References
\$a = \$b; # $a and $b now point to the same scalar
\&foo = \&bar; # foo() now means bar()
-This syntax must be enabled with C<use feature 'lvalue_refs'>. It is
+This syntax must be enabled with C<use feature 'refaliasing'>. It is
experimental, and will warn by default unless C<no warnings
-'experimental::lvalue_refs'> is in effect.
+'experimental::refaliasing'> is in effect.
These forms may be assigned to, and cause the right-hand side to be
evaluated in scalar context:
\local $some_hash{$key}
condition ? \$this : \$that[0] # etc.
-Parentheses cause the right-hand side to be evaluated in list context:
+Slicing operations and parentheses cause
+the right-hand side to be evaluated in
+list context:
+ \@array[5..7]
+ (\@array[5..7])
+ \(@array[5..7])
+ \@hash{'foo','bar'}
+ (\@hash{'foo','bar'})
+ \(@hash{'foo','bar'})
(\$scalar)
\($scalar)
\(my $scalar)
# @harry is (1,2,3)
my $type = ref $thingy;
- ($type ? $type == 'ARRAY' ? \@foo : \$bar : $baz) = $thingy;
+ ($type ? $type eq 'ARRAY' ? \@foo : \$bar : $baz) = $thingy;
The C<foreach> loop can also take a reference constructor for its loop
variable, though the syntax is limited to one of the following, with an
}
foreach \my %h (@array_of_hashes) {
- $h{gelastic}++ if $h{type} == 'funny';
+ $h{gelastic}++ if $h{type} eq 'funny';
}
B<CAVEAT:> Aliasing does not work correctly with closures. If you try to
https://perl5.git.perl.org / perl5.git / blobdiff