[Seaside-dev] exception handler instance creation

[Julian Fitzell]

I started writing some docs on the new exception handler interface. In
doing so, I realized I hated the method name #exceptionToCatch so I
changed that and then remembered that Lukas was asking for the
exception handlers to implement #handles: and #, so that they can be
used in place of an ExceptionSet as defined in the ANSI spec. So I did
this too.

This raised again the question of when an instance of our exception
handlers should be created. If you look at the current implementation
of #handleExceptionsDuring:context:, you will see that an instance is
not actually created until an exception that this class handles is
signaled. This requires a temporary variable and means that the
instance does not have a chance to indicate whether it wants to handle
the exception or not (whether they is a required feature or not is
perhaps debatable... I dunno).

The only reason I did this was to avoid the overhead of creating the
instance when we don't need it but I'm wondering if this was a
premature optimization and the implementation would be simpler if I
didn't do it. #handleExceptionsDuring:context: would just become:

#handleExceptionsDuring: aBlock context: aRequestContext
   ^ (self context: aRequestContext) handleExceptionsDuring: aBlock

And on the instance side we would have:

#handleExceptionsDuring: aBlock
	^ aBlock
		on: self
		do: [ :exception |
			[ self handleException: exception ]
				on: Error
				do: [ :error | self internalError: error ] ]

No temporary variable, instances can choose whether to handle
exceptions if they want to, no risk of being unable to create an error
handler when reporting an internal error.

Am I right that this seems like the better option?

Julian