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.\" ========================================================================
.\"
.IX Title "base 3"
.TH base 3 "2019-10-24" "perl v5.30.2" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification. Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
base \- Establish an ISA relationship with base classes at compile time
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\& package Baz;
\& use base qw(Foo Bar);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
Unless you are using the \f(CW\*(C`fields\*(C'\fR pragma, consider this module discouraged
in favor of the lighter-weight \f(CW\*(C`parent\*(C'\fR.
.PP
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
.PP
.Vb 6
\& package Baz;
\& BEGIN {
\& require Foo;
\& require Bar;
\& push @ISA, qw(Foo Bar);
\& }
.Ve
.PP
When \f(CW\*(C`base\*(C'\fR tries to \f(CW\*(C`require\*(C'\fR 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, \f(CW\*(C`base\*(C'\fR 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:
.PP
.Vb 3
\& # in Bar.pm
\& package Foo;
\& sub exclaim { "I can have such a thing?!" }
\&
\& package Bar;
\& use base "Foo";
.Ve
.PP
There is no \fIFoo.pm\fR, but because \f(CW\*(C`Foo\*(C'\fR defines a symbol (the \f(CW\*(C`exclaim\*(C'\fR
subroutine), \f(CW\*(C`base\*(C'\fR will not die when the \f(CW\*(C`require\*(C'\fR fails to load \fIFoo.pm\fR.
.PP
\&\f(CW\*(C`base\*(C'\fR will also initialize the fields if one of the base classes has it.
Multiple inheritance of fields is \fB\s-1NOT\s0\fR supported, if two or more base classes
each have inheritable fields the 'base' pragma will croak. See fields
for a description of this feature.
.PP
The base class' \f(CW\*(C`import\*(C'\fR method is \fBnot\fR called.
.SH "DIAGNOSTICS"
.IX Header "DIAGNOSTICS"
.ie n .IP "Base class package ""%s"" is empty." 4
.el .IP "Base class package ``%s'' is empty." 4
.IX Item "Base class package %s is empty."
base.pm was unable to require the base package, because it was not
found in your path.
.IP "Class 'Foo' tried to inherit from itself" 4
.IX Item "Class 'Foo' tried to inherit from itself"
Attempting to inherit from yourself generates a warning.
.Sp
.Vb 2
\& package Foo;
\& use base \*(AqFoo\*(Aq;
.Ve
.SH "HISTORY"
.IX Header "HISTORY"
This module was introduced with Perl 5.004_04.
.SH "CAVEATS"
.IX Header "CAVEATS"
Due to the limitations of the implementation, you must use
base \fIbefore\fR you declare any of your own fields.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
fields