Help with associative arrays

Help with associative arrays

[Vin Shelton]

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I can't seem to figure this out.  I'm trying to use an associative array
and the results are not what I expect:

#!/usr/bin/env zsh

emulate -LR zsh

typeset -A repos
repos["conky"]="https://github.com/brndnmtthws/conky.git"

nickname="conky"
echo "nickname = " \"$nickname\" "repos = " \"${repos[$nickname]}\"
echo "nickname = " \"$nickname\" "repos = " \"${repos["conky"]}\"

yileds:

nickname =  "conky" repos =  ""
nickname =  "conky" repos =  "https://github.com/brndnmtthws/conky.git"

given that nickname is "conky" I expected the values to be the same.

Puzzled,
  Vin

Re: Help with associative arrays

[Lawrence Velázquez]

> On Aug 21, 2016, at 4:50 PM, Vin Shelton <ethersoft@gmail.com> wrote:
> 
> I can't seem to figure this out.  I'm trying to use an associative
> array and the results are not what I expect:
> 
> #!/usr/bin/env zsh
> 
> emulate -LR zsh
> 
> typeset -A repos
> repos["conky"]="https://github.com/brndnmtthws/conky.git"
> 
> nickname="conky"
> echo "nickname = " \"$nickname\" "repos = " \"${repos[$nickname]}\"
> echo "nickname = " \"$nickname\" "repos = " \"${repos["conky"]}\"
> 
> yileds:
> 
> nickname =  "conky" repos =  ""
> nickname =  "conky" repos =  "https://github.com/brndnmtthws/conky.git"
> 
> given that nickname is "conky" I expected the values to be the same.

From zshparam(1):

        The basic rule to remember when writing a subscript expression
        is that all text between the opening `[' and the closing `]' is
        interpreted as if it were in double quotes (see zshmisc(1)).

        [...]

        The second difference is that a double-quote (`"') may appear as
        part of a subscript expression without being preceded by
        a backslash....

The double quotes you're using are not acting as quoting syntax; they
are being treated literally and are becoming part of the key itself.

	% typeset -A repos1; repos1["conky"]=foo; typeset repos1
	repos1=( '"conky"' foo )
	% typeset -A repos2; repos2[conky]=foo; typeset repos2
	repos2=( conky foo )

But the quotes are behaving as you expect when you do the assignment to
"nickname".

	% nickname="conky"; typeset nickname
	nickname=conky

So $repos[$nickname] is evaluated as $repos[conky], not $repos["conky"],
while your array contains a '"conky"' key, not a 'conky' key. In the
end, you're not looking up the key you want.

tl;dr: Don't use double quotes in array subscripts, unless your array
contains keys with literal double quotes.

vq

Re: Help with associative arrays

[Vin Shelton]

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I will quote only the summary, but the explanation was well worthwhile.

On Sun, Aug 21, 2016 at 5:18 PM, Lawrence Velázquez <vq@larryv.me> wrote:

> tl;dr: Don't use double quotes in array subscripts, unless your array
> contains keys with literal double quotes.
>

Yes, thank you, that works.

  - Vin

Re: Help with associative arrays

[Stephane Chazelas]

2016-08-21 17:18:11 -0400, Lawrence Velázquez:
[...]
>         The second difference is that a double-quote (`"') may appear as
>         part of a subscript expression without being preceded by
>         a backslash....
[...]

An annoying consequence is that (contrary to with ksh93) you can't do:

a[""]=foo

To assign an element for the empty key. You have to do things
like:

a[${}]=foo

or

a+=('' foo)

instead.

It would be nice if one could do:

a[]=foo

(which currently returns an error)

Note that it's a lot worse in bash. bash associative arrays
can't have an element with an empty key!

-- 
Stephane