[squeak-dev] Re-signalling an already signaled exception
mail at jaromir.net
mail at jaromir.net
Sat Feb 5 17:48:39 UTC 2022
On 2022-02-04T17:11:35-06:00, asqueaker at gmail.com wrote:
> Hi Jaromir,
> Here's a motivation example:
> > [1/0] on: Error do: [:ex |
> > [ex signal] on: ZeroDivide do: [Transcript show: #ZeroDivide]
> > ]
> > Would you expect this code to work and pick up the ZeroDivide handler?
> > The point or a use case is to provide additional (finer, more specific)
> > handlers inside the general handler rather than wrap the general handler
> > inside more specific handlers. More specific handlers can even be inside a
> > method so the readability would not degrade.
> I was able to do it by creating a new exception instance and signaling it:
> [1/0] on: Error do: [: err |
> [err copy signal] on: ZeroDivide do: [Transcript show:
> #ZeroDivide] ]
> I don't know about #copy, though, you might want to implement your own
> special #freshCopy that throws out the signalContext, handlerContext and
> outerContext, but the above "worked". :)
Precisely, it crossed my mind too and yes, it has to be a "fresh" copy with blank instance variables (except messageText). A simple copy fails tests with nested outer etc...
I've checked ANSI again and they say, quote: [220.127.116.11 messageText][...] Subsequent sends of of the message #messageText to a signaled exception generated by sending the message #signal to the receiver of this message [note: the receiver is an exception instance] will also return this value.
So what I'm actually looking for is this: (and it's equivalent to the "fresh" copy idea)
[1/0] on: Error do: [: err |
[err class signal: err messageText] on: ZeroDivide do: [Transcript show: #ZeroDivide] ]
If I'm interpreting ANSI's intention correctly then we could update our #signal like this:
"Ask ContextHandlers in the sender chain to handle this signal. The default is to execute and return my defaultAction.
Signaling an already signaled exception is interpreted as signaling a new exception of the same type with the same messageText"
- signalContext ifNotNil: [^self outer].
+ signalContext ifNotNil: [^self copy signal: self messageText].
signalContext := thisContext contextTag.
^(thisContext nextHandlerContextForSignal: self) handleSignal: self
It was my idea last year to make subsequent sends of #signal to an already signaled exception equivalent to #outer and now I can see it was wrong and I'd like to really fix it this time :) All test are green, even the ones in Tests-jar.464.
Thanks, Chris, for discussing this.
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