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

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Roughly similar in effect to</p> <pre><code>package Baz; BEGIN { require Foo; require Bar; push @ISA, qw(Foo Bar); }</code></pre> <p><code>base</code> employs some heuristics to determine if a module has already been loaded, if it has it doesn't try again. If <code>base</code> tries to <code>require</code> the 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, it will die. This is useful for inheriting from classes in the same file as yourself, like so:</p> <pre><code>package Foo; sub exclaim { "I can have such a thing?!" } package Bar; use base "Foo";</code></pre> <p>If $VERSION is not detected even after loading it, <base> will define $VERSION in the base package, setting it to the string <code>-1, set by base.pm</code>.</p> <p><code>base</code> will also initialize the fields if one of the base classes has it. Multiple inheritance of fields is <b>NOT</b> supported, if two or more base classes each have inheritable fields the 'base' pragma will croak. See <a href="/5.10.1/fields">fields</a>, <a href="/5.10.1/public">public</a> and <a href="/5.10.1/protected">protected</a> for a description of this feature.</p> <p>The base class' <code>import</code> method is <b>not</b> called.</p> <h1 id="DIAGNOSTICS"><a class="permalink" href="#DIAGNOSTICS">#</a>DIAGNOSTICS</h1> <dl> <dt id="Base-class-package-"%s"-is-empty."><a class="permalink" href="#Base-class-package-%22%25s%22-is-empty.">#</a><a id="Base"></a><a id="Base-class-package-s-is-empty"></a>Base class package "%s" is empty.</dt> <dd> <p>base.pm was unable to require the base package, because it was not found in your path.</p> </dd> <dt id="Class-'Foo'-tried-to-inherit-from-itself"><a class="permalink" href="#Class-'Foo'-tried-to-inherit-from-itself">#</a><a id="Class"></a><a id="Class-Foo-tried-to-inherit-from-itself"></a>Class 'Foo' tried to inherit from itself</dt> <dd> <p>Attempting to inherit from yourself generates a warning.</p> <pre><code>use Foo; use base 'Foo';</code></pre> </dd> </dl> <h1 id="HISTORY"><a class="permalink" href="#HISTORY">#</a>HISTORY</h1> <p>This module was introduced with Perl 5.004_04.</p> <h1 id="CAVEATS"><a class="permalink" href="#CAVEATS">#</a>CAVEATS</h1> <p>Due to the limitations of the implementation, you must use base <i>before</i> you declare any of your own fields.</p> <h1 id="SEE-ALSO"><a class="permalink" href="#SEE-ALSO">#</a><a id="SEE"></a>SEE ALSO</h1> <p><a href="/5.10.1/fields">fields</a></p> </div> <div id="footer"> <p>Perldoc Browser is maintained by Dan Book (<a href="https://metacpan.org/author/DBOOK">DBOOK</a>). 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base - Establish an ISA relationship with base classes at compile time - Perldoc Browser