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Re: Changing the way bash expands associative array subscripts

From: Chet Ramey
Subject: Re: Changing the way bash expands associative array subscripts
Date: Thu, 8 Apr 2021 14:33:45 -0400
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On 4/6/21 1:55 AM, Koichi Murase wrote:
2021年3月30日(火) 0:03 Chet Ramey <chet.ramey@case.edu>:
On 3/15/21 9:41 PM, Koichi Murase wrote:
Can you also take care of the behavior of `unset -v 'a[@]''?

Well, you have to pick one behavior or another. The `@' subscript always
expands to all members of the array. The current behavior is consistent
with that, and documented.

When `shopt -s assoc_expand_once' is enabled, I think it is better
that `unset -v 'a[@]'' will remove just an element associated with the
key `@' but not remove the entire associative array `a' although it
might be inconsistent to the other places such as `${a[@]}'.

Why with `assoc_expand_once'? Would it not be just as surprising, or more,
to have a `@' remove the entire array if it were the target of the much-
hated `double expansion'? That's part of what we're talking about fixing.

We're having this discussion in the context of assoc_expand_once, or its
effects, being enabled all the time. I agree that those changes are not
needed to have `@' not remove the entire array, but I'm still planning to
move forward with the changes we started out discussing.

specifically, I'm thinking of the use case that a user wants to remove
an entry for an arbitrary $key using

   unset -v "assoc[$key]"

I agree, that's what we're talking about here. But you don't need this:

But, maybe we can introduce a special syntactic treatment of `unset'
as done for `declare/typeset/local/export/readonly'. Just as ${a[@]}
and ${a[$key]} are treated differently, maybe we can treat

   unset -v a[@]


   unset -v a[$key]


to achieve that.

I'm not going to make unset a reserved word. It's not necessary.

Yes. If there isn't a strong reason for disallowing the empty
associative-array keys, may I create a new thread of bug-bash for the
feature request of supporting empty keys?

Sure, let's discuss it.

``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    chet@case.edu    http://tiswww.cwru.edu/~chet/

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