bindings-overloading.html
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"><title>Overloading and optional arguments</title><meta name="generator" content="DocBook XSL Stylesheets V1.68.1"><link rel="start" href="index.html" title="Cairo: A Vector Graphics Library"><link rel="up" href="language-bindings.html" title="Appendix A. Creating a language binding for cairo"><link rel="prev" href="bindings-return-values.html" title="Multiple return values"><link rel="next" href="bindings-streams.html" title="Streams and File I/O"><meta name="generator" content="GTK-Doc V1.6 (XML mode)"><link rel="stylesheet" href="style.css" type="text/css"><link rel="part" href="pt01.html" title="Part I. Tutorial"><link rel="part" href="pt02.html" title="Part II. Reference"><link rel="chapter" href="Drawing.html" title="Drawing"><link rel="chapter" href="Fonts.html" title="Fonts"><link rel="chapter" href="Surfaces.html" title="Surfaces"><link rel="chapter" href="Support.html" title="Utilities"><link rel="index" href="ix01.html" title="Index"><link rel="appendix" href="language-bindings.html" title="Appendix A. Creating a language binding for cairo"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><table class="navigation" id="top" width="100%" summary="Navigation header" cellpadding="2" cellspacing="2"><tr valign="middle"><td><a accesskey="p" href="bindings-return-values.html"><img src="left.png" width="24" height="24" border="0" alt="Prev"></a></td><td><a accesskey="u" href="language-bindings.html"><img src="up.png" width="24" height="24" border="0" alt="Up"></a></td><td><a accesskey="h" href="index.html"><img src="home.png" width="24" height="24" border="0" alt="Home"></a></td><th width="100%" align="center">Cairo: A Vector Graphics Library</th><td><a accesskey="n" href="bindings-streams.html"><img src="right.png" width="24" height="24" border="0" alt="Next"></a></td></tr></table><div class="sect1" lang="en"><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 href="cairo-cairo-t.html#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">voidcairo_set_source (cairo_t *cr, cairo_pattern_t *source);voidcairo_set_source_surface (cairo_t *cr, cairo_surface_t *source, double surface_x, double surface_y); voidcairo_mask (cairo_t *cr, cairo_pattern_t *pattern);voidcairo_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_tcairo_surface_write_to_png (cairo_surface_t *surface, const char *filename);cairo_status_tcairo_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 href="cairo-PNG-Support.html#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 href="cairo-Image-Surfaces.html#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">voidcairo_move_to (cairo_t *cr, cairo_point_t *point);voidcairo_rectangle (cairo_t *cr, cairo_rectangle_t *rectangle); </pre></div></body></html>⌨️ 快捷键说明
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