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  3. <title>SWIG:Examples:perl5:class</title>
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  7. 

  8. 

  9. <tt>SWIG/Examples/perl5/class/</tt>
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  10. <hr>
    11. 

  11. 

  12. <H2>Wrapping a simple C++ class</H2>
    13. 

  13. 

  14. <p>
    15. 

  15. This example illustrates the most primitive form of C++ class wrapping performed
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  16. by SWIG.  In this case, C++ classes are simply transformed into a collection of
    17. 

  17. C-style functions that provide access to class members.
    18. 

  18. 

  19. <h2>The C++ Code</h2>
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  20. 

  21. Suppose you have some C++ classes described by the following (and admittedly lame) 
    22. 

  22. header file:
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  23. 

  24. <blockquote>
    25. 

  25. <pre>
    26. 

  26. /* File : example.h */
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  27. 

  28. class Shape {
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  29. public:
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  30.   Shape() {
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  31.     nshapes++;
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  32.   }
    33. 

  33.   virtual ~Shape() {
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  34.     nshapes--;
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  35.   };
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  36.   double  x, y;   
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  37.   void    move(double dx, double dy);
    38. 

  38.   virtual double area() = 0;
    39. 

  39.   virtual double perimeter() = 0;
    40. 

  40.   static  int nshapes;
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  41. };
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  42. 

  43. class Circle : public Shape {
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  44. private:
    45. 

  45.   double radius;
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  46. public:
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  47.   Circle(double r) : radius(r) { };
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  48.   virtual double area();
    49. 

  49.   virtual double perimeter();
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  50. };
    51. 

  51. 

  52. class Square : public Shape {
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  53. private:
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  54.   double width;
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  55. public:
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  56.   Square(double w) : width(w) { };
    57. 

  57.   virtual double area();
    58. 

  58.   virtual double perimeter();
    59. 

  59. };
    60. 

  60. </pre>
    61. 

  61. </blockquote>
    62. 

  62. 

  63. <h2>The SWIG interface</h2>
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  64. 

  65. A simple SWIG interface for this can be built by simply grabbing the header file
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  66. like this:
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  67. 

  68. <blockquote>
    69. 

  69. <pre>
    70. 

  70. /* File : example.i */
    71. 

  71. %module example
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  72. 

  73. %{
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  74. #include "example.h"
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  75. %}
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  76. 

  77. /* Let's just grab the original header file here */
    78. 

  78. %include "example.h"
    79. 

  79. </pre>
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  80. </blockquote>
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  81. 

  82. Note: when creating a C++ extension, you must run SWIG with the <tt>-c++</tt> option like this:
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  83. <blockquote>
    84. 

  84. <pre>
    85. 

  85. % swig -c++ -python example.i
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  86. </pre>
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  87. </blockquote>
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  88. 

  89. <h2>A sample Perl script</h2>
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  90. 

  91. Click <a href="runme.pl">here</a> to see a script that calls the C++ functions from Perl.
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  92. 

  93. <h2>Key points</h2>
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  94. 

  95. <ul>
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  96. <li>To create a new object, you call a constructor like this:
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  97. 

  98. <blockquote>
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  99. <pre>
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  100. $c = example::new_Circle(10.0);
    101. 

  101. </pre>
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  102. </blockquote>
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  103. 

  104. <p>
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  105. <li>To access member data, a pair of accessor functions are used.
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  106. For example:
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  107. 

  108. <blockquote>
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  109. <pre>
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  110. example::Shape_x_set($c,15);    # Set member data
    111. 

  111. $x = example::Shape_x_get($c);   # Get member data
    112. 

  112. </pre>
    113. 

  113. </blockquote>
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  114. 

  115. Note: when accessing member data, the name of the class in which
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  116. the data member is defined is used.  For example <tt>Shape_x_get()</tt>.
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  117. 

  118. <p>
    119. 

  119. <li>To invoke a member function, you simply do this
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  120. 

  121. <blockquote>
    122. 

  122. <pre>
    123. 

  123. print "The area is ", example::Shape_area($c);
    124. 

  124. </pre>
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  125. </blockquote>
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  126. 

  127. <p>
    128. 

  128. <li>Type checking knows about the inheritance structure of C++. For example:
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  129. 

  130. <blockquote>
    131. 

  131. <pre>
    132. 

  132. example::Shape_area($c);       # Works (c is a Shape)
    133. 

  133. example::Circle_area($c);      # Works (c is a Circle)
    134. 

  134. example::Square_area($c);      # Fails (c is definitely not a Square)
    135. 

  135. </pre>
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  136. </blockquote>
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  137. 

  138. <p>
    139. 

  139. <li>To invoke a destructor, simply do this
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  140. 

  141. <blockquote>
    142. 

  142. <pre>
    143. 

  143. example::delete_Shape($c);     # Deletes a shape
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  144. </pre>
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  145. </blockquote>
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  146. 

  147. <p>
    148. 

  148. <li>Static member variables are wrapped as C global variables.  For example:
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  149. 

  150. <blockquote>
    151. 

  151. <pre>
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  152. $n = $example::Shape_nshapes;     # Get a static data member
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  153. $example::Shapes_nshapes = 13;   # Set a static data member
    154. 

  154. </pre>
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  155. </blockquote>
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  156. 

  157. </ul>
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  158. 

  159. <h2>General Comments</h2>
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  160. 

  161. <ul>
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  162. <li>This low-level interface is not the only way to handle C++ code.  Proxy classes
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  163. provide a much higher-level interface.
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  164. 

  165. <p>
    166. 

  166. <li>SWIG *does* know how to properly perform upcasting of objects in an inheritance
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  167. hierarchy (including multiple inheritance).  Therefore it is perfectly safe to pass
    168. 

  168. an object of a derived class to any function involving a base class.
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  169. 

  170. <p>
    171. 

  171. <li>A wide variety of C++ features are not currently supported by SWIG.  Here is the
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  172. short and incomplete list:
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  173. 

  174. <p>
    175. 

  175. <ul>
    176. 

  176. <li>Overloaded methods and functions.  SWIG wrappers don't know how to resolve name
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  177. conflicts so you must give an alternative name to any overloaded method name using the
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  178. %name directive like this:
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  179. 

  180. <blockquote>
    181. 

  181. <pre>
    182. 

  182. void foo(int a);  
    183. 

  183. %name(foo2) void foo(double a, double b);
    184. 

  184. </pre>
    185. 

  185. </blockquote>
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  186. 

  187. <p>
    188. 

  188. <li>Overloaded operators.  Not supported at all. The only workaround for this is
    189. 

  189. to write a helper function. For example:
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  190. 

  191. <blockquote>
    192. 

  192. <pre>
    193. 

  193. %inline %{
    194. 

  194.     Vector *vector_add(Vector *a, Vector *b) {
    195. 

  195.           ... whatever ...
    196. 

  196.     }
    197. 

  197. %}
    198. 

  198. </pre>
    199. 

  199. </blockquote>
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  200. 

  201. <p>
    202. 

  202. <li>Namespaces.  Not supported at all. Won't be supported until SWIG2.0 (if at all).
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    204. 

  204. </ul>
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  205. 

  206. <hr>
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  207. </body>
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  208. </html>
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  209.