This is a topic I originally mentioned in another discussion on the
new treatment of assoc_expand_once (
https://lists.gnu.org/archive/html/bug-bash/2021-03/msg00059.html ).
As in the mail subject, I suggest supporting empty keys for
associative arrays. Does anyone have any opinion on this suggestion?
Description:
Currently, associative arrays do not accept empty keys. We can work
it around e.g. by always prefixing `x' before the keys, such as
`assoc[x$key]=$value'. But I still think we may support empty keys
for associative arrays because I don't see strong reasons to disallow
the empty keys of associative arrays. Here is the quote of the
original discussion:
2021年3月16日(火) 10:41 Koichi Murase <myoga.mur...@gmail.com>:
> Maybe this is unrelated to the extra expansions of array subscripts,
> but is there any reason that Bash disallows empty associative keys?
> This is also a point that confuses users related to the keys of
> associative arrays. Associative arrays in other languages usually
> accept an empty key. I usually use `a[x$key]' for the workaround, but
> I personally feel we should support empty associative keys in Bash. I
> also remember that at least two other people were confused by the
> current behavior not accepting the empty key.
Repeat-By:
Here I summarize the current behavior for the empty keys. It seems
Bash already parses empty keys for assignments, but they seem to be
afterward rejected:
$ declare -A a=()
$ a[]=1
bash-dev: a[]: bad array subscript
$ a['']=1
bash-dev: a['']: bad array subscript
`a[]' in parameter expansions are not parsed. The variant `a['']'
pass through the parsing phase but is later rejected:
$ echo ${a[]}
bash-dev: ${a[]}: bad substitution
$ echo ${a['']}
bash-dev: a: bad array subscript
The variable name `a[]' is rejected in `printf -v', indirect
expansions, and namerefs:
$ printf -v 'a[]' 1
bash-dev: printf: `a[]': not a valid identifier
$ printf -v 'a[""]' 1
bash-dev: a[""]: bad array subscript
$ iref='a[]'; echo ${!iref}
bash-dev: a[]: invalid variable name
$ iref='a[""]'; echo ${!iref}
bash-dev: a: bad array subscript
$ declare -n nref='a[]'; echo $nref
bash-dev: declare: `a[]': invalid variable name for name reference
$ declare -n nref='a[""]'; echo $nref
bash-dev: a: bad array subscript
No error message for `unset 'a[]''?
$ unset 'a[]'
$ unset 'a[""]'
bash-dev: unset: [""]: bad array subscript
--
Koichi
