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* error.c (Init_Exception): Document $! and $@. Provide

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recommendations for creating exceptions for a library.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@33482 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
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drbrain 2011-10-19 02:52:38 +00:00
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@ -1,3 +1,8 @@
Wed Oct 19 11:48:44 2011 Eric Hodel <drbrain@segment7.net>
* error.c (Init_Exception): Document $! and $@. Provide
recommendations for creating exceptions for a library.
Wed Oct 19 11:25:46 2011 Eric Hodel <drbrain@segment7.net>
* error.c (Init_Exception): Add hierarchy of Exception subclasses.

46
error.c
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@ -1522,14 +1522,44 @@ syserr_eqq(VALUE self, VALUE exc)
*/
/*
* Descendants of class <code>Exception</code> are used to communicate
* between <code>raise</code> methods and <code>rescue</code>
* statements in <code>begin/end</code> blocks. <code>Exception</code>
* objects carry information about the exception---its type (the
* exception's class name), an optional descriptive string, and
* optional traceback information. Programs may subclass
* <code>Exception</code>, or more typically <code>StandardError</code>
* to provide custom classes and add additional information.
* Descendants of class Exception are used to communicate between
* Kernel#raise and +rescue+ statements in <code>begin ... end</code> blocks.
* Exception objects carry information about the exception -- its type (the
* exception's class name), an optional descriptive string, and optional
* traceback information. Exception subclasses may add additional
* information like NameError#name.
*
* Programs may make subclasses of Exception, typically of StandardError or
* RuntimeError, to provide custom classes and add additional information.
* See the subclass list below for defaults for +raise+ and +rescue+.
*
* When an exception has been raised but not yet handled (in +rescue+,
* +ensure+, +at_exit+ and +END+ blocks) the global variable <code>$!</code>
* will contain the current exception and <code>$@</code> contains the
* current exception's backtrace.
*
* It is recommended that a library should have one subclass of StandardError
* or RuntimeError and have specific exception types inherit from it. This
* allows the user to rescue a generic exception type to catch all exceptions
* the library may raise even if future versions of the library add new
* exception subclasses.
*
* For example:
*
* class MyLibrary
* class Error < RuntimeError
* end
*
* class WidgetError < Error
* end
*
* class FrobError < Error
* end
*
* end
*
* To handle both WidgetError and FrobError the library user can rescue
* MyLibrary::Error.
*
* The built-in subclasses of Exception are:
*