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bug#25166: 26.0.50; It shouldn't be possible to set the function cell of


From: Philipp Stephani
Subject: bug#25166: 26.0.50; It shouldn't be possible to set the function cell of nil and t
Date: Mon, 26 Dec 2016 19:29:17 +0000



Glenn Morris <rgm@gnu.org> schrieb am Mo., 12. Dez. 2016 um 21:25 Uhr:
Glenn Morris wrote:

> Philipp wrote:
>
>> You can set the function cell of nil and t using `fset' and friends.
>> But you can't call the `nil' function using (nil) (it does work with
>> (t)).  I think that attempting to set the function cell of nil and t is
>> almost always a bug -- probably the programmer wanted to set a real
>> symbol, but some of the constants got passed.  I propose to signal an
>> error (e.g. `setting-constant') whenever the function cell of nil and t
>> is modified; maybe the same should happen for keywords.
>
> I just did this yesterday...
> See https://debbugs.gnu.org/25110, ba8e883, and 3fd4433.

And now see also ffb1302. :)
Anyway, I only did "nil", since as you say "t" can actually be called as
a function. But you are right that it's probably unintended.


Thanks! Interestingly the behavior was already added in 1994 (commit c15c5d408d696928862ca2848a359231e373556c), but apparently reverted later. I'd suggest to simply reinstate that commit. 

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