NAME

       ExtUtils::XSpp::Exception - Map C++ exceptions to Perl exceptions

DESCRIPTION

       This class is both the base class for the different exception handling mechanisms and the
       container for the global set of exception mappings from C++ exceptions (indicated by a C++
       data type to catch) to Perl exceptions. The Perl exceptions are implemented via "croak()".

       The basic idea is that you can declare the C++ exception types that you want to handle and
       how you plan to do so by using the %exception directive in your XS++ (or better yet, in
       the XS++ typemap):

         // OutOfBoundsException would have been declared
         // elsewhere as:
         //
         // class OutOfBoundsException : public std::exception {
         // public:
         //   OutOfBoundsException() {}
         //   virtual const char* what() const throw() {
         //     return "You accessed me out of bounds, fool!";
         //   }
         // }

         %exception{outOfBounds}{OutOfBoundsException}{stdmessage};

       If you know a function or method may throw "MyOutOfBoundsException"s, you can annotate the
       declaration in your XS++ as follows:

         double get_from_array(unsigned int index)
           %catch{outOfBounds};

       When "get_from_array" now throws an "OutOfBoundsException", the user gets a Perl croak
       with the message "Caught exception of type 'OutOfBoundsException': You accessed me out of
       bounds, fool!".  There may be any number of %catch directives per method.

       Note: Why do we assign another name ("outOfBounds") to the existing
       "OutOfBoundsException"?  Because you may need to catch exceptions of the same C++ type
       with different handlers for different methods. You can, in principle, re-use the C++
       exception class name for the exception map name, but that may be confusing to posterity.

       Instead of adding %catch to methods, you may also specify exceptions that you wish to
       handle for all methods of a class:

         class Foo %catch{SomeException,AnotherException} {
           ...
         };

       The %catch{Foo,Bar,...} syntax is shorthand for "%catch{Foo} %catch{Bar} ...".  If there
       are exceptions to be caught both from the class and attached to a method directly, the
       exceptions that are attached to the method only will be handled first. No single type of
       exceptions will be handled more than once, therefore it is safe to use this precedence to
       re-order the class-global exception handling for a single method.

       If there are no %catch decorators on a method, exceptions derived from "std::exception"
       will be caught with a generic "stdmessage" handler such as above. Even if there are %catch
       clauses for the given method, all otherwise uncaught exceptions will be caught with a
       generic error message for safety.

Exception handlers

       There are different cases of Perl exceptions that are implemented as sub-classes of
       "ExtUtils::XSpp::Exception":

       ExtUtils::XSpp::Exception::simple
         implements the most general case of simply throwing a generic error message that
         includes the name of the C++ exception type.

       ExtUtils::XSpp::Exception::stdmessage
         handles C++ exceptions that are derived from "std::exception" and which provide a "char*
         what()" method that will provide an error message.  The Perl-level error message will
         include the C++ exception type name and the exception's "what()" message.

       ExtUtils::XSpp::Exception::code
         allows the user to supply custom C/C++/XS code that will be included in the exception
         handler verbatim. The code has access to the exception object as the variable "e". Your
         user supplied code is expected to propagate the exception to Perl by calling croak().

       ExtUtils::XSpp::Exception::object
         maps C++ exceptions to throwing an instance of some Perl exception class.

         Syntax:

           %exception{myClassyException}{CppException}{object}{PerlClass};

         Currently, this means just calling "PerlClass->new()" and then die()ing with that object
         in $@. There is no good way to pass information from the C++ exception object to the
         Perl object.  Will change in future.

       ExtUtils::XSpp::Exception::unknown
         is the default exception handler that is added to the list of handlers automatically
         during code generation. It simply throws an entirely unspecific error and catches the
         type "..." (meaning anything).

       There is a special exception handler "nothing" which is always available:

         int foo() %catch{nothing};

       It indicates that the given method (or function) is to handle no exceptions. It squishes
       any exception handlers that might otherwise be inherited from the method's class.

METHODS

   new
       Creates a new "ExtUtils::XSpp::Exception".

       Calls the "$self->init(@_)" method after construction.  "init()" must be overridden in
       subclasses.

   handler_code
       Unimplemented in this base class, but must be implemented in all actual exception classes.

       Generates the "catch(){}" block of code for inclusion in the XS output. First (optional)
       argument is an integer indicating the number of spaces to use for the first indentation
       level.

   indent_code
       Given a piece of code and a number of spaces to use for global indentation, indents the
       code and returns it.

   cpp_type
       Fetches the C++ type of the exception from the "type" attribute and returns it.

ACCESSORS

   name
       Returns the name of the exception.  This is the "myException" in
       %exception{myException}{char*}{handler}.

   type
       Returns the ExtUtils::XSpp::Node::Type C++ type that is used for this exception.  This is
       the "char*" in %exception{myException}{char*}{handler}.

CLASS METHODS

   add_exception
       Given an "ExtUtils::XSpp::Exception" object, adds this object to the global registry,
       potentially overwriting an exception map of the same name that was in effect before.

   get_exception_for_name
       Given the XS++ name of the exception map, fetches the corresponding
       "ExtUtils::XSpp::Exception" object from the global registry and returns it. Croaks on
       error.