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.