An our declares the listed variables to be valid globals within the
enclosing block, file, or eval. That is, it has the same scoping rules as a
"my" declaration, but does not create a local variable. If more than one value
is listed, the list must be placed in parentheses. The our declaration has no
semantic effect unless "use strict vars" is in effect, in which case it lets you
use the declared global variable without qualifying it with a package name. (But only
within the lexical scope of the our declaration. In this it differs from
"use vars", which is package scoped.)
An our declaration declares a global variable that will be visible across
its entire lexical scope, even across package boundaries. The package in which the
variable is entered is determined at the point of the declaration, not at the point of
use. This means the following behavior holds:
package Foo;
our $bar; # declares $Foo::bar for rest of lexical scope
$bar = 20;
package Bar;
print $bar; # prints 20
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Multiple our declarations in the same lexical scope are allowed if they
are in different packages. If they happened to be in the same package, Perl will emit
warnings if you have asked for them.
use warnings;
package Foo;
our $bar; # declares $Foo::bar for rest of lexical scope
$bar = 20;
package Bar;
our $bar = 30; # declares $Bar::bar for rest of lexical scope
print $bar; # prints 30
our $bar; # emits warning
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An our declaration may also have a list of attributes associated with it.
The exact semantics and interface of TYPE and ATTRS are still evolving. TYPE is
currently bound to the use of fields pragma, and attributes are handled using
the attributes pragma, or starting from Perl 5.8.0 also via the Attribute::Handlers
module. See perlsub/"Private
Variables via my()" for details, and fields, attributes, and Attribute::Handlers.
The only currently recognized our() attribute is unique which
indicates that a single copy of the global is to be used by all interpreters should the
program happen to be running in a multi-interpreter environment. (The default behaviour
would be for each interpreter to have its own copy of the global.) Examples:
our @EXPORT : unique = qw(foo);
our %EXPORT_TAGS : unique = (bar => [qw(aa bb cc)]);
our $VERSION : unique = "1.00";
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Note that this attribute also has the effect of making the global readonly when the
first new interpreter is cloned (for example, when the first new thread is created).
Multi-interpreter environments can come to being either through the fork() emulation on
Windows platforms, or by embedding perl in a multi-threaded application. The unique
attribute does nothing in all other environments.
