NAME

base - Establish an ISA relationship with base classes at compile time

SYNOPSIS

    package Baz;
    use base qw(Foo Bar);

DESCRIPTION

Unless you are using the fields pragma, consider this module discouraged in favor of the lighter-weight parent.

Allows you to both load one or more modules, while setting up inheritance from those modules at the same time. Roughly similar in effect to

    package Baz;
    BEGIN {
        require Foo;
        require Bar;
        push @ISA, qw(Foo Bar);
        Internals::SvREADONLY(@ISA, 1); # cperl only
    }

When base tries to require a module, it will not die if it cannot find the module's file, but will die on any other error. After all this, should your base class be empty, containing no symbols, base will die. This is useful for inheriting from classes in the same file as yourself but where the filename does not match the base module name, like so:

        # in Bar.pm
        package Foo;
        sub exclaim { "I can have such a thing?!" }

        package Bar;
        use base "Foo";

There is no Foo.pm, but because Foo defines a symbol (the exclaim subroutine), base will not die when the require fails to load Foo.pm.

base will also initialize the fields if one of the base classes has it. Multiple inheritance of fields is NOT supported, if two or more base classes each have inheritable fields the 'base' pragma will croak. See fields for a description of this feature.

The base class' import method is not called.

use base is also important to allow compile-time type checks on user classes. Without base the type-checker doesn't know if the class @ISA is closed already, and will not find parents being added later at run-time.

DIAGNOSTICS

Base class package "%s" is empty.

base.pm was unable to require the base package, because it was not found in your path.

Class 'Foo' tried to inherit from itself

Attempting to inherit from yourself generates a warning.

    package Foo;
    use base 'Foo';

HISTORY

This module was introduced with Perl 5.004_04.

CAVEATS

Due to the limitations of the implementation, you must use base before you declare any of your own fields.