Examples/ruby/class/index.html

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<title>SWIG:Examples:ruby:class</title>
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<tt>SWIG/Examples/ruby/class/</tt>
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<H2>Wrapping a simple C++ class</H2>

<p>
This example illustrates wrapping a simple C++ class to give a Ruby class.

<h2>The C++ Code</h2>

Suppose you have some C++ classes described by the following (and admittedly lame) 
header file:

<blockquote>
<pre>
/* File : example.h */

class Shape {
public:
  Shape() {
    nshapes++;
  }
  virtual ~Shape() {
    nshapes--;
  }
  double  x, y;
  void    move(double dx, double dy);
  virtual double area() = 0;
  virtual double perimeter() = 0;
  static  int nshapes;
};

class Circle : public Shape {
private:
  double radius;
public:
  Circle(double r) : radius(r) { }
  virtual double area();
  virtual double perimeter();
};

class Square : public Shape {
private:
  double width;
public:
  Square(double w) : width(w) { }
  virtual double area();
  virtual double perimeter();
};
</pre>
</blockquote>

<h2>The SWIG interface</h2>

A simple SWIG interface for this can be built by simply grabbing the header file
like this:

<blockquote>
<pre>
/* File : example.i */
%module example

%{
#include "example.h"
%}

/* Let's just grab the original header file here */
%include "example.h"
</pre>
</blockquote>

Note: when creating a C++ extension, you must run SWIG with the <tt>-c++</tt> option like this:
<blockquote>
<pre>
% swig -c++ -ruby example.i
</pre>
</blockquote>

<h2>A sample Ruby script</h2>

Click <a href="runme.rb">here</a> to see a script that calls the C++ functions from Ruby.

<h2>Key points</h2>

<ul>
<li>To create a new object, you call a constructor like this:

<blockquote>
<pre>
c = Example::Circle.new(10)
</pre>
</blockquote>

<p>
<li>To access member data, a pair of accessor methods are used.
For example:

<blockquote>
<pre>
c.x = 15    # Set member data
x = c.x     # Get member data
</pre>
</blockquote>

<p>
<li>To invoke a member function, you simply do this

<blockquote>
<pre>
print "The area is ", c.area, "\n"
</pre>
</blockquote>

<p>
<li>When a instance of Ruby level wrapper class is garbage collected by the
Ruby interpreter, the corresponding C++ destructor is automatically invoked.

<p>
<li>Static member variables are wrapped as Ruby class accessor methods.
For example:

<blockquote>
<pre>
n = Shape.nshapes     # Get a static data member
Shapes.nshapes = 13   # Set a static data member
</pre>
</blockquote>

</ul>

<h2>General Comments</h2>

<ul>
<li>Ruby module of SWIG differs from other language modules in wrapping C++
interfaces.  They provide lower-level interfaces and optional higher-level
interfaces know as proxy classes.  Ruby module needs no such redundancy
due to Ruby's sophisticated extension API.

<li>SWIG <b>does</b> know how to properly perform upcasting of objects in
an inheritance hierarchy except for multiple inheritance.

<li>C++ Namespaces - %nspace isn't yet supported for Ruby.

</ul>

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