Re: `apply-partially` and hash tables

[<tomas@tuxteam.de>]

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On Sun, Oct 20, 2024 at 11:43:15AM +0200, Joost Kremers wrote:
> Hi list,
> 
> A question that just came up: if I use `apply-partially` to create a
> function that has a hash table as one of its fixed arguments, and then at
> some later point add data to said hash table, it seems that this data is
> visible to subsequent calls to the partially applied function:
> 
> ```
> (let* ((s #s(hash-table test equal data ("MGrt" "Mouton De Gruyter"
>                                          "OTS" "Utrecht School of Linguistics UiL-OTS")))
>        (fn (apply-partially #'parsebib--expand-strings s)))
>   (puthash "BW" "Oxford: Blackwell Publishers" s)
>   (funcall fn "BW"))
> "Oxford: Blackwell Publishers"
> ```
> 
> `parsebib--expand-strings` is a function that (among other things) does a
> hash table look-up. The entry ("BW" "Oxford: Blackwell Publishers") is
> added to the hash table after the function is created, but it can obviously
> still be found by it.
> 
> So my question: is this intended behaviour, something that I can rely on to
> continue to work, or is this an artefact of the implementation that may
> change at any time in the future?

This is an interesting question: it comes down to what can be considered
"immutable".

I guess a hash table doesn't count (as wouldn't a buffer, possibly a list
or any other object with a complex "inner life").

Cheers
-- 
t

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