Scope modifiers: Difference between revisions
→{{header|Perl}}: Reintegrated the discussion of 'state'.
(→{{header|R}}: substantially expanded discussion) |
Underscore (talk | contribs) (→{{header|Perl}}: Reintegrated the discussion of 'state'.) |
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By default, an unqualified name refers to a package variable in the current package. The current package is whatever you set it to with the last <code>package</code> declaration in the current lexical scope, or <code>main</code> by default. But wherever stricture is in effect, using a name that would be resolved this way is a compile-time error.
There are three kinds of declaration that can influence the scoping of a particular variable: <code>our</code>, <code>my</code>, <code>state</code>, and <code>local</code>. <code>our</code> makes a package variable lexically available. Its primary use is to allow easy access to package variables under stricture.
<lang perl>use strict;
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print "$fruit\n"; # Prints "orange"; refers to $Bar::fruit.
# The first $fruit is inaccessible.</lang>
<code>state</code> is like <code>my</code> but creates a variable only once. The variable's value is remembered between visits to the enclosing scope. The <code>state</code> feature is only available in perl 5.9.4 and later, and must be activated with <code>use feature 'state';</code> or a <code>use</code> demanding a sufficiently recent perl.
<lang perl>use 5.10.0;▼
{
state $foo = 13;▼
say $foo++;▼
}▼
count_up; # Prints "13".
count_up; # Prints "14".</lang>
<code>local</code> gives a package variable a new value for the duration of the current ''dynamic'' scope.
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}
phooey; # Prints "llama".
sub do_phooey
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}
do_phooey; # Prints "alpaca".
phooey; # Prints "llama".</lang>
Usually, <code>my</code> is preferrable to <code>local</code>, but one thing <code>local</code> can do that <code>my</code> can't is affect the special punctuation variables, like <code>$/</code> and <code>$"</code>. Actually, in perl 5.9.1 and later, <code>my $_</code> is specially allowed and works as you would expect.
▲<lang perl>
▲sub count_up{
▲ state $foo;
▲ $foo++;
▲}
=={{header|PicoLisp}}==
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