There is a usecount on each value, but that doesn't help here, because
the usecount is not incremented when the value is referenced, but only
when it is assigned (it's too hard to change that, at least for now).
But there is a stack of names that are 'in play' - have been referenced
by this or a higher-level sentence. The trick would be to look in this
stack, in higher sentences, to see if the name being assigned is in use.
Since in-place update is not a guarantee, I think it could be documented
with a page describing what makes in-place update possible. I am hoping
to use in-place update much more than we have previously done, so such a
page would be needed anyway. It is a Coding Tip rather than a Language
Description.
Henry
On 6/21/2016 1:21 PM, Raul Miller wrote:
That fix you describe seems reasonable - I think it winds up being an
"in use counter" on each name which, in effect, caches the result that
you would get by walking the stack counting references.
Documenting this issue, however, probably warrants some thought. How
do you explain to people that the same code will run quickly or slowly
depending on the calling environment? Since "global" variable use is
also a code correctness and design issue, I do not think the
performance issue raised by fix you describe makes it be a bad
language design decision (though of course there will be critics of
any design decision).
Anyways... a quick search suggests a few mentions which probably need
elaboration on this subject (perhaps something like: "as of version
___ a problem was resolved where in place assignment conflicted with
the dictionary definition. Note also that this means that if a
sentence is using a name and calling some code which would otherwise
have been doing an in place update of that name that in place
assignment would be inconsistent for the caller and does not happen.
This is both a performance and a code correctness issue." - but if
someone could come up with a better phrasing, that would probably be a
good thing). Here's the references I found which will eventually need
updating:
http://code.jsoftware.com/wiki/Vocabulary/curlyrt
http://www.jsoftware.com/help/jforc/modifying_an_array_m.htm
http://code.jsoftware.com/wiki/Vocabulary/SpecialCombinations
http://www.jsoftware.com/help/jforc/performance_measurement__tip.htm
Nothing is ever simple, which I guess is a part of why we put so much
effort into trying to make things right...
Thanks,
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