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<title>The HarfBuzz object model: HarfBuzz Manual</title>
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<div class="chapter">
<div class="titlepage"><div><div><h2 class="title">
<a name="object-model"></a>The HarfBuzz object model</h2></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="section"><a href="object-model.html#object-model-intro">An overview of data types in HarfBuzz</a></span></dt>
<dt><span class="section"><a href="object-model-object-types.html">Objects in HarfBuzz</a></span></dt>
<dt><span class="section"><a href="object-model-lifecycle.html">Object lifecycle management</a></span></dt>
<dt><span class="section"><a href="object-model-user-data.html">User data</a></span></dt>
<dt><span class="section"><a href="object-model-blobs.html">Blobs</a></span></dt>
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="object-model-intro"></a>An overview of data types in HarfBuzz</h2></div></div></div>
<p>
HarfBuzz features two kinds of data types: non-opaque,
pass-by-value types and opaque, heap-allocated types. This kind
of separation is common in C libraries that have to provide
API/ABI compatibility (almost) indefinitely.
</p>
<p>
<span class="emphasis"><em>Value types:</em></span> The non-opaque, pass-by-value
types include integer types, enums, and small structs. Exposing
a struct in the public API makes it impossible to expand the
struct in the future. As such, exposing structs is reserved for
cases where it’s extremely inefficient to do otherwise.
</p>
<p>
In HarfBuzz, several structs, like <code class="literal">hb_glyph_info_t</code> and
<code class="literal">hb_glyph_position_t</code>, fall into that efficiency-sensitive
category and are non-opaque.
</p>
<p>
For all non-opaque structs where future extensibility may be
necessary, reserved members are included to hold space for
possible future members. As such, it’s important to provide
<code class="function">equal()</code>, and <code class="function">hash()</code>
methods for such structs, allowing users of the API do
effectively deal with the type without having to
adapt their code to future changes.
</p>
<p>
Important value types provided by HarfBuzz include the structs
for working with Unicode code points, glyphs, and tags for font
tables and features, as well as the enums for many Unicode and
OpenType properties.
</p>
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