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<title>Cairo: A Vector Graphics Library: Overloading and optional arguments</title>
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<div class="sect1">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="bindings-overloading"></a>Overloading and optional arguments</h2></div></div></div>
<p>
Function overloading (having a several variants of a function
with the same name and different arguments) is a language
feature available in many languages but not in C.
</p>
<p>
In general, language binding authors should use restraint in
combining functions in the cairo API via function
overloading. What may seem like an obvious overload now may
turn out to be strange with future additions to cairo.
It might seem logical to make
<a class="link" href="cairo-cairo-t.html#cairo-set-source-rgb" title="cairo_set_source_rgb ()"><code class="function">cairo_set_source_rgb()</code></a>
an overload of <code class="function">cairo_set_source()</code>, but future plans to add
<code class="function">cairo_set_source_rgb_premultiplied()</code>,
which will also take three doubles make this a bad idea. For
this reason, only the following pairs of functions should
be combined via overloading
</p>
<pre class="programlisting">
void
cairo_set_source (cairo_t *cr, cairo_pattern_t *source);
void
cairo_set_source_surface (cairo_t *cr,
cairo_surface_t *source,
double surface_x,
double surface_y);
void
cairo_mask (cairo_t *cr,
cairo_pattern_t *pattern);
void
cairo_mask_surface (cairo_t *cr,
cairo_surface_t *surface,
double surface_x,
double surface_y);
cairo_surface_t *
cairo_image_surface_create (cairo_format_t format,
int width,
int height);
cairo_surface_t *
cairo_image_surface_create_for_data (unsigned char *data,
cairo_format_t format,
int width,
int height,
int stride);
cairo_status_t
cairo_surface_write_to_png (cairo_surface_t *surface,
const char *filename);
cairo_status_t
cairo_surface_write_to_png_stream (cairo_surface_t *surface,
cairo_write_func_t write_func,
void *closure);
cairo_surface_t *
cairo_image_surface_create_from_png (const char *filename);
cairo_surface_t *
cairo_image_surface_create_from_png_stream (cairo_read_func_t read_func,
void *closure);
</pre>
<p>
Note that there are cases where all constructors for a type
aren't overloaded together. For example
<a class="link" href="cairo-PNG-Support.html#cairo-image-surface-create-from-png" title="cairo_image_surface_create_from_png ()"><code class="function">cairo_image_surface_create_from_png()</code></a>
should <span class="emphasis"><em>not</em></span> be overloaded together with
<a class="link" href="cairo-Image-Surfaces.html#cairo-image-surface-create" title="cairo_image_surface_create ()"><code class="function">cairo_image_surface_create()</code></a>.
In such cases, the remaining constructors will typically need to
be bound as static methods. In Java, for example, we might have:
</p>
<pre class="programlisting">
Surface surface1 = ImageSurface(Format.RGB24, 100, 100);
Surface surface2 = ImageSurface.createFromPNG("camera.png");</pre>
<p>
Some other overloads that add combinations not found in C may be
convenient for users for language bindings that provide
<span class="type">cairo_point_t</span> and <span class="type">cairo_rectangle_t</span>
types, for example:
</p>
<pre class="programlisting">
void
cairo_move_to (cairo_t *cr,
cairo_point_t *point);
void
cairo_rectangle (cairo_t *cr,
cairo_rectangle_t *rectangle);
</pre>
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