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Re: Associative array keys are not reusable in (( command

From: Koichi Murase
Subject: Re: Associative array keys are not reusable in (( command
Date: Fri, 8 Jan 2021 19:14:13 +0800

This topic actually pops up occasionally.  FYI, you can also see the
following discussions:


2021年1月8日(金) 18:21 Oğuz <oguzismailuysal@gmail.com>:
> `(( assoc[\$key]++ ))' works as usual, but this is not documented as
> far as I know,

This is explained in the first link above by quoting two sentences in
the document, but I agree with you that this is so non-trivial that
it's worth explicitly documenting IMHO.

> Considering that the following two works, it doesn't make much sense
> that `(( assoc[$key]++ ))' doesn't.

I think the POSIX expansion order should be applied to, for example,
$((assoc[$key]++)).  In this case, the arithmetic evaluation of the
whole expression should be performed only after $key in
$((assoc[$key]++)) is expanded.  There is no reason to introduce a
different expansion rule of `((...))' from that of `$((...))'.  It
feels a bit strange to me to expand `$key' in `(( assoc[$key]++ ))'
after determining the arithmetic structure thinking the normal
expansion order.

> It would be better if at least quoting the key by means of parameter
> transformation or `printf %q' worked, because these are the first
> workarounds that come to mind;

This is maybe a good idea.  From Bash 5.1, the single quotation is
not a subject to the quote removal of `(( ... ))', so we can use the
single quotation as a part of the arithmetic expression.  We can just
introduce the string literal of the form '...' or $'...' in the
arithmetic evaluator.


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