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Tue Jul 13 17:19:59 CEST 2004 · https://mail.python.org/pipermail/python-dev/2004-July/046119.html

Tim Peters wrote:
> [Jim Fulton, on non-zero return values from a visitproc]
> 
...

>>First, I don't like this macro, based on my own experience writing macros
>>that hide returns. :)
> 
> 
> Except VISIT is useful only inside a tp_traverse implementation, and
> all such implementations look exactly the same (VISIT, VISIT, VISIT,
> ..., sometimes with a surrounding loop).  That's not an accident,
> since the only purpose of a tp_traverse implementation is to VISIT
> containees.  So it's a special-purpose macro for a highly specific and
> uniform task, not a general-purpose macro that has to play well in
> arbitrary contexts.

I still don't like it, because it hides the return.

I'd rather do:

	if (self->foo != NULL && (vret = visit(self->foo, arg)))
		return vret;

than

         VISIT(self->foo)

So I'm not interested in the macro myself. :)

I'll say again that I don't like calling the return from the visit
proc an error indicator, because it's not, and because it goes against
the common idiom of using a negative return to indicate an error.
I think that these common idioms are important, because they help
us understand the code we're reading more easily.

Jim

-- 
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