<html> <head> <title>SWIG:Examples:ruby:class</title> </head> <body bgcolor="#ffffff"> <tt>SWIG/Examples/ruby/class/</tt> <hr> <H2>Wrapping a simple C++ class</H2> <tt>$Header: /cvs/projects/SWIG/Examples/ruby/class/index.html,v 1.1.4.1 2001/08/30 10:48:04 cheetah Exp $</tt><br> <p> This example illustrates C++ class wrapping performed by SWIG. C++ classes are simply transformed into Ruby classes that provide methods to access class members. <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 Ruby interpreter, the corresponding C++ destructor is automatically invoked. (Note: destructors are currently not inherited. This might change later. Until then, use <tt>-make_default</tt>). <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 provides lower-level interfaces and optional higher-level interfaces know as shadow classes. Ruby module needs no such redundancy due to Ruby's sophisticated extension API. <p> <li>SWIG *does* know how to properly perform upcasting of objects in an inheritance hierarchy except for multiple inheritance. <p> <li>A wide variety of C++ features are not currently supported by SWIG. Here is the short and incomplete list: <p> <ul> <li>Overloaded methods and functions. SWIG wrappers don't know how to resolve name conflicts so you must give an alternative name to any overloaded method name using the %name directive like this: <blockquote> <pre> void foo(int a); %name(foo2) void foo(double a, double b); </pre> </blockquote> <p> <li>Overloaded operators. Not supported at all. The only workaround for this is to write a helper function. For example: <blockquote> <pre> %inline %{ Vector *vector_add(Vector *a, Vector *b) { ... whatever ... } %} </pre> </blockquote> <p> <li>Namespaces. Not supported at all. Won't be supported until SWIG2.0 (if at all). </ul> <p> <li>Dave's snide remark: Like a large bottle of strong Tequilla, it's better to use C++ in moderation. </ul> <hr> </body> </html>