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<title>Tie::ExtraHash - base class definitions for tied hashes</title>
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<h1><a>Tie::ExtraHash - base class definitions for tied hashes</a></h1>
<p><a name="__index__"></a></p>
<!-- INDEX BEGIN -->
<ul>
<li><a href="#name">NAME</a></li>
<li><a href="#synopsis">SYNOPSIS</a></li>
<li><a href="#description">DESCRIPTION</a></li>
<li><a href="#inheriting_from_tie__stdhash">Inheriting from <strong>Tie::StdHash</strong></a></li>
<li><a href="#inheriting_from_tie__extrahash">Inheriting from <strong>Tie::ExtraHash</strong></a></li>
<li><a href="#scalar__untie_and_destroy"><code>SCALAR</code>, <code>UNTIE</code> and <code>DESTROY</code></a></li>
<li><a href="#more_information">MORE INFORMATION</a></li>
</ul>
<!-- INDEX END -->
<hr />
<p>
</p>
<h1><a name="name">NAME</a></h1>
<p>Tie::Hash, Tie::StdHash, Tie::ExtraHash - base class definitions for tied hashes</p>
<p>
</p>
<hr />
<h1><a name="synopsis">SYNOPSIS</a></h1>
<pre>
<span class="keyword">package</span> <span class="variable">NewHash</span><span class="operator">;</span>
<span class="keyword">require</span> <span class="variable">Tie::Hash</span><span class="operator">;</span>
</pre>
<pre>
<span class="variable">@ISA</span> <span class="operator">=</span> <span class="operator">(</span><span class="variable">Tie::Hash</span><span class="operator">);</span>
</pre>
<pre>
<span class="keyword">sub</span><span class="variable"> DELETE </span><span class="operator">{</span> <span class="operator">...</span> <span class="operator">}</span> <span class="comment"># Provides needed method</span>
<span class="keyword">sub</span><span class="variable"> CLEAR </span><span class="operator">{</span> <span class="operator">...</span> <span class="operator">}</span> <span class="comment"># Overrides inherited method</span>
</pre>
<pre>
<span class="keyword">package</span> <span class="variable">NewStdHash</span><span class="operator">;</span>
<span class="keyword">require</span> <span class="variable">Tie::Hash</span><span class="operator">;</span>
</pre>
<pre>
<span class="variable">@ISA</span> <span class="operator">=</span> <span class="operator">(</span><span class="variable">Tie::StdHash</span><span class="operator">);</span>
</pre>
<pre>
<span class="comment"># All methods provided by default, define only those needing overrides</span>
<span class="comment"># Accessors access the storage in %{$_[0]};</span>
<span class="comment"># TIEHASH should return a reference to the actual storage</span>
<span class="keyword">sub</span><span class="variable"> DELETE </span><span class="operator">{</span> <span class="operator">...</span> <span class="operator">}</span>
</pre>
<pre>
<span class="keyword">package</span> <span class="variable">NewExtraHash</span><span class="operator">;</span>
<span class="keyword">require</span> <span class="variable">Tie::Hash</span><span class="operator">;</span>
</pre>
<pre>
<span class="variable">@ISA</span> <span class="operator">=</span> <span class="operator">(</span><span class="variable">Tie::ExtraHash</span><span class="operator">);</span>
</pre>
<pre>
<span class="comment"># All methods provided by default, define only those needing overrides</span>
<span class="comment"># Accessors access the storage in %{$_[0][0]};</span>
<span class="comment"># TIEHASH should return an array reference with the first element being</span>
<span class="comment"># the reference to the actual storage </span>
<span class="keyword">sub</span><span class="variable"> DELETE </span><span class="operator">{</span>
<span class="variable">$_</span><span class="operator">[</span><span class="number">0</span><span class="operator">][</span><span class="number">1</span><span class="operator">]</span><span class="operator">->(</span><span class="string">'del'</span><span class="operator">,</span> <span class="variable">$_</span><span class="operator">[</span><span class="number">0</span><span class="operator">][</span><span class="number">0</span><span class="operator">]</span><span class="operator">,</span> <span class="variable">$_</span><span class="operator">[</span><span class="number">1</span><span class="operator">]</span><span class="operator">);</span> <span class="comment"># Call the report writer</span>
<span class="keyword">delete</span> <span class="variable">$_</span><span class="operator">[</span><span class="number">0</span><span class="operator">][</span><span class="number">0</span><span class="operator">]</span><span class="operator">-></span><span class="operator">{</span><span class="variable">$_</span><span class="operator">[</span><span class="number">1</span><span class="operator">]}</span><span class="operator">;</span> <span class="comment"># $_[0]->SUPER::DELETE($_[1])</span>
<span class="operator">}</span>
</pre>
<pre>
<span class="keyword">package</span> <span class="variable">main</span><span class="operator">;</span>
</pre>
<pre>
<span class="keyword">tie</span> <span class="variable">%new_hash</span><span class="operator">,</span> <span class="string">'NewHash'</span><span class="operator">;</span>
<span class="keyword">tie</span> <span class="variable">%new_std_hash</span><span class="operator">,</span> <span class="string">'NewStdHash'</span><span class="operator">;</span>
<span class="keyword">tie</span> <span class="variable">%new_extra_hash</span><span class="operator">,</span> <span class="string">'NewExtraHash'</span><span class="operator">,</span>
<span class="keyword">sub</span><span class="variable"> </span><span class="operator">{</span><span class="keyword">warn</span> <span class="string">"Doing \U$_[1]\E of $_[2].\n"</span><span class="operator">};</span>
</pre>
<p>
</p>
<hr />
<h1><a name="description">DESCRIPTION</a></h1>
<p>This module provides some skeletal methods for hash-tying classes. See
<a href="../../lib/Pod/perltie.html">the perltie manpage</a> for a list of the functions required in order to tie a hash
to a package. The basic <strong>Tie::Hash</strong> package provides a <code>new</code> method, as well
as methods <code>TIEHASH</code>, <code>EXISTS</code> and <code>CLEAR</code>. The <strong>Tie::StdHash</strong> and
<strong>Tie::ExtraHash</strong> packages
provide most methods for hashes described in <a href="../../lib/Pod/perltie.html">the perltie manpage</a> (the exceptions
are <code>UNTIE</code> and <code>DESTROY</code>). They cause tied hashes to behave exactly like standard hashes,
and allow for selective overwriting of methods. <strong>Tie::Hash</strong> grandfathers the
<code>new</code> method: it is used if <code>TIEHASH</code> is not defined
in the case a class forgets to include a <code>TIEHASH</code> method.</p>
<p>For developers wishing to write their own tied hashes, the required methods
are briefly defined below. See the <a href="../../lib/Pod/perltie.html">the perltie manpage</a> section for more detailed
descriptive, as well as example code:</p>
<dl>
<dt><strong><a name="item_tiehash_classname_2c_list">TIEHASH classname, LIST</a></strong>
<dd>
<p>The method invoked by the command <code>tie %hash, classname</code>. Associates a new
hash instance with the specified class. <code>LIST</code> would represent additional
arguments (along the lines of <a href="../../lib/AnyDBM_File.html">the AnyDBM_File manpage</a> and compatriots) needed to
complete the association.</p>
</dd>
</li>
<dt><strong><a name="item_store_this_2c_key_2c_value">STORE this, key, value</a></strong>
<dd>
<p>Store datum <em>value</em> into <em>key</em> for the tied hash <em>this</em>.</p>
</dd>
</li>
<dt><strong><a name="item_fetch_this_2c_key">FETCH this, key</a></strong>
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