Re: This errors in 4.4, did not in 4.2: set -u; declare -A foo; echo ${#foo[@]}

[#!microsuxx]

On Thu, Nov 7, 2024, 21:10 Chet Ramey <chet.ramey@case.edu> wrote:

> On 11/6/24 9:38 PM, David Linden wrote:
>
> > Bash Version: 4.4
> > Patch Level: 20
> > Release Status: release
> >
> > Description:
> >       This errors in 4.4, did not in 4.2: set -u; declare -A foo; echo
> ${#foo[@]}
>
> Yes, this was a bug in bash-4.2, fixed in bash-4.3. A variable isn't set
> until it's been assigned a value. This fix aligns the array variable
> behavior with the scalar (non-array) variable behavior.
>
>
> >       How am I supposed to determine that a declared associative array
> is empty?
>

to try to answer ' how to check if assoc arr is empty '
first [[ ${name@a} == *A* ]] or == A not sure

then in code

~/m $ cat m.test.emptyassoc
#!/bin/bash

 c() {
local r=$@
eval -- "$r"
l
 }

 l() {
l1
 }

 r() {
eval "$@" &&
echo -e "$@\t\t$r"
  }

 l1() {
r [[ -v $n ]]
r "(( \${#$n[@]} ))"
 }

unset -v assoc n
n=assoc

c : init
c declare -A assoc
c 'assoc+=( foo bar )'
c 'assoc+=( 2foo 2bar )'
c unset -v $n

~/m $ bash m.test.emptyassoc
[[ -v assoc ]]          assoc+=( foo bar )
(( ${#assoc[@]} ))              assoc+=( foo bar )
[[ -v assoc ]]          assoc+=( 2foo 2bar )
(( ${#assoc[@]} ))              assoc+=( 2foo 2bar )

therefore [[ -v and (( $# works

That's not the question that `set -u' answers. It will tell you whether
> a variable with attributes (or without) has been assigned a value.
>
> Does your code manage this variable? If it does, you should be able to
> determine whether or not it was ever assigned a value, or make sure
> that it has been assigned a value, if that's important. The empty array
> is a valid value, just like the empty string is a valid value for scalar
> variables.
>
> >       Or even use it in a conditional even one where the value won't be
> evaluated?
>

what

What do you mean? Using something like foo[@] is fine in expansions
> where it won't be expanded:
>
> echo ${foo[@]-unset}
>
> or
>
> v=set; echo ${v:-foo[@]}
>
> But if you get into a case where the variable needs to be expanded,
> you're going to get an error if the variable isn't set.
>
> --
> ``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/
>