| <html> |
| <head> |
| <title>SWIG:Examples:ruby:class</title> |
| </head> |
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| <body bgcolor="#ffffff"> |
| |
| |
| <tt>SWIG/Examples/ruby/class/</tt> |
| <hr> |
| |
| <H2>Wrapping a simple C++ class</H2> |
| |
| <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 proxy 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> |