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Re: quoted compound array assignment deprecated


From: Chet Ramey
Subject: Re: quoted compound array assignment deprecated
Date: Wed, 19 Aug 2015 10:07:46 -0400
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:38.0) Gecko/20100101 Thunderbird/38.0.1

On 8/18/15 5:05 PM, Dan Douglas wrote:
> Sorry I meant to reply to that thread but ran out of time. I think Stephane's 
> eventual proposal was pretty close to what I had in mind but expressed badly. 
> I'm not sure why it was eventually decided to deprecate the current system 
> entirely but I'm not opposed to the idea - especially if it provides no 
> functionality for which there aren't easy workarounds.

Deprecated doesn't mean removed.  In this case, the meaning is closer to
discouraged or deemphasized.

Bash understands `declare' as a Posix declaration utility, and does its
best to treat arguments to declare and other declaration utilities
identically to standalone assignment statements.  The place where that
breaks down is if a compound array assignment is treated as such by
declare when it would have been treated as a scalar assignment had it
appeared standalone.  That's why the warning.  It's not an error.


> The only thing I'm actively abusing this for at the moment in scripts I 
> actually use is as a way of encoding 2D arrays. It's very much a read-only 
> datastructure too.
> 
> ~ $ ( key1=foo key2=bar; declare -A a=([foo]='([bar]=baz)') "b=${a[$key1]}"
> typeset -p a b; echo "${b[$key2]}" )
> declare -A a='([foo]="([bar]=baz)" )'
> declare -A b='([bar]="baz" )'
> baz
> 
> Any change will likely break this property but I think wrapping it in eval 
> gives the same result.

This will continue to work, but with a warning about a potentially
dangerous construct.


-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU    address@hidden    http://cnswww.cns.cwru.edu/~chet/



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