New example showing use of %catchs and %

git-svn-id: https://swig.svn.sourceforge.net/svnroot/swig/trunk/SWIG@8355 626c5289-ae23-0410-ae9c-e8d60b6d4f22

Examples/ruby/exception_class/example.i

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+/* This example illustrates the use of the %exceptionclass feature.  By
+   default, if a method has a throws specification then SWIG will generate
+   code to catch the exception and pass it on the scripting language.
+   
+   If a method does not have a throws specification, but does throw 
+   an exception, then the %exceptionclass feature can be used to tell
+   SWIG about the exception class so it can be properly added to Ruby.
+   This is done by making the exception class inherit from rb_eRuntimeError.*/
+
+%module example
+
+%{
+#include "example.h"
+%}
+
+
+/* The EmpytError doesn't appear in a throw declaration, and hence
+  we need to tell SWIG that the dequeue method throws it.  This can
+  now be done via the %catchs feature. */
+%catchs(EmptyError) *::dequeue();
+
+
+/* What the catchs clause is doing under the covers is this:
+
+%exceptionclass EmptyError;
+
+%exception *::dequeue {
+   try {
+      $action
+   } catch(EmptyError& e) {
+		  // Create a new instance of the EmptyError, wrap it as a Ruby object that Ruby owns,
+		  // and return it as the exception.  For this to work EmtpyError must inherit from
+		  // a standard Ruby exception class such as rb_eRuntimeError.  SWIG automatically does
+		  // this when the class is marked as %exceptionclass or is a throws specification.
+ 		%raise(SWIG_NewPointerObj(new EmptyError(e), SWIGTYPE_p_EmptyError, SWIG_POINTER_OWN), "EmptyError", SWIGTYPE_p_EmptyError);
+   }
+}
+*/
+
+/* Grab the original header file */
+%include "example.h"
+
+/* Instantiate a few templates */
+%template(IntQueue) Queue<int>;
+%template(DoubleQueue) Queue<double>;