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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="object-model-user-data"></a>User data</h2></div></div></div>
<p>
To better integrate with client programs, HarfBuzz's objects
offer a "user data" mechanism that can be used to attach
arbitrary data to the object. User-data attachment can be
useful for tying the lifecycles of various pieces of data
together, or for creating language bindings.
</p>
<p>
Each object type has a <code class="function">set_user_data()</code>
method and a <code class="function">get_user_data()</code> method. The
<code class="function">set_user_data()</code> methods take a client-provided
<code class="literal">key</code> and a pointer,
<code class="literal">user_data</code>, pointing to the data itself. Once
the key-data pair has been attached to the object, the
<code class="function">get_user_data()</code> method can be called with
the key, returning the <code class="function">user_data</code> pointer.
</p>
<p>
The <code class="function">set_user_data()</code> methods also support an
optional <code class="function">destroy</code> callback. Client programs
can set the <code class="function">destroy</code> callback and receive
notification from HarfBuzz whenever the object is destructed.
</p>
<p>
Finally, each <code class="function">set_user_data()</code> method allows
the client program to set a <code class="literal">replace</code> Boolean
indicating whether or not the function call should replace any
existing <code class="literal">user_data</code>
associated with the specified key.
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