Re: +=() can be used to set illegal indices

[Emanuele Torre]

On Fri, Jun 30, 2023 at 12:16:46PM -0400, Chet Ramey wrote:
> > What I would have expected was something like this:
> > 
> >    $ x=([9223372036854775805]=foo)
> >    $ x+=( {1..5} ); echo "this won't run"
> >    bash: some "invalid assignment" error
> >    $ declare -p x # no value gets appended since there was an error
> 
> No. Why wouldn't the valid assignments be accepted? If you want
> 
> a=(1 2 3)
> 
> to be as close as possible to
> 
> a[0]=1
> a[1]=2
> a[2]=3
> 
> you have to do it that way.

Hmm, I have never noticed that behaviour to be honest.

I would have expected:

  $ a=([1]=hi [100]=foo [-1002]=bar boo [200]=baz); echo "won't run"
  bash: [-1002]=bar: bad array subscript
  $ declare -p a
  bash: declare: a: not found

But it seems bash actually behaves like so:

  $ a=([1]=hi [100]=foo [-1002]=bar boo [200]=baz); echo "will run"
  bash: [-1002]=bar: bad array subscript
  will run
  $ declare -p a
  declare -a a=([1]="hi" [100]="foo" [101]="boo" [200]="baz")

So it simply skips and prints a warning for invalid indices, and still
sets all the other valid indices, without triggering an error for the
assignment; even though  a[-1002]=bar  on its own would have triggered
an error:

  $ a[1]=hi a[100]=foo a[-1002]=bar a[200]=baz; echo "won't run"
  bash: [-1002]=bar: bad array subscript
  $ declare -p a
  declare -a a=([1]="hi" [100]="foo")

The ksh behaviour is more similar to a sequence of a[k1]=v1 a[k2]=v2
assignments; only the assignments before the first invalid index are
performed, and the assignment triggers an error (n.b. you need to use
typeset -a  with ksh93 otherwise it creates an associative array if you
use  a=([k1]=v1 [k2]=v2)  ):

  $ typeset -a a=([1]=hi [100]=foo [-1002]=bar [200]=baz); echo "won't run"
  ksh: a: subscript out of range
  $ typeset -p a
  typeset -a a=([1]=hi [100]=foo)

Anyhow, if x+=() should behave similarly to  x=( ... ), I guess my
example should work like so:

  $ x=([9223372036854775805]=foo)
  $ x+=( {1..5} ); echo "will run"
  bash: x[-9223372036854775808]: bad array subscript
  bash: x[-9223372036854775807]: bad array subscript
  bash: x[-9223372036854775806]: bad array subscript
  will run
  $ echo "${x[@]}"
  foo 1 2


o/
 emanuele6