Perl 5 version 24.0 documentation


  • our VARLIST


    our makes a lexical alias to a package (i.e. global) variable of the same name in the current package for use within the current lexical scope.

    our has the same scoping rules as my or state, meaning that it is only valid within a lexical scope. Unlike my and state, which both declare new (lexical) variables, our only creates an alias to an existing variable: a package variable of the same name.

    This means that when use strict 'vars' is in effect, our lets you use a package variable without qualifying it with the package name, but only within the lexical scope of the our declaration. This applies immediately--even within the same statement.

    1. package Foo;
    2. use strict;
    3. $Foo::foo = 23;
    4. {
    5. our $foo; # alias to $Foo::foo
    6. print $foo; # prints 23
    7. }
    8. print $Foo::foo; # prints 23
    9. print $foo; # ERROR: requires explicit package name

    This works even if the package variable has not been used before, as package variables spring into existence when first used.

    1. package Foo;
    2. use strict;
    3. our $foo = 23; # just like $Foo::foo = 23
    4. print $Foo::foo; # prints 23

    Because the variable becomes legal immediately under use strict 'vars' , so long as there is no variable with that name is already in scope, you can then reference the package variable again even within the same statement.

    1. package Foo;
    2. use strict;
    3. my $foo = $foo; # error, undeclared $foo on right-hand side
    4. our $foo = $foo; # no errors

    If more than one variable is listed, the list must be placed in parentheses.

    1. our($bar, $baz);

    An our declaration declares an alias for a package 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:

    1. package Foo;
    2. our $bar; # declares $Foo::bar for rest of lexical scope
    3. $bar = 20;
    4. package Bar;
    5. print $bar; # prints 20, as it refers to $Foo::bar

    Multiple our declarations with the same name in the same lexical scope are allowed if they are in different packages. If they happen to be in the same package, Perl will emit warnings if you have asked for them, just like multiple my declarations. Unlike a second my declaration, which will bind the name to a fresh variable, a second our declaration in the same package, in the same scope, is merely redundant.

    1. use warnings;
    2. package Foo;
    4. $bar = 20;
    5. package Bar;
    6. our $bar = 30; # declares $Bar::bar for rest of lexical scope
    7. print $bar; # prints 30
    8. our $bar; # emits warning but has no other effect
    9. print $bar; # still prints 30

    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 the fields pragma, and attributes are handled using the attributes pragma, or, starting from Perl 5.8.0, also via the Attribute::Handlers module. See Private Variables via my() in perlsub for details.

    Note that with a parenthesised list, undef can be used as a dummy placeholder, for example to skip assignment of initial values:

    1. our ( undef, $min, $hour ) = localtime;

    our differs from use vars , which allows use of an unqualified name only within the affected package, but across scopes.