Explicit variables declaration statements do not resolve back-references from same statement

[Léa Gris]

Found this strange behavior difference in Bash, between explicit and 
implicit declarations of variables.

An implicit variables declaration statement resolve back-references to 
variables from the same statement.

Whereas:

An explicit variables declaration statement does not resolve 
back-reference variables from the same statement.

Illustration code:

==== knip code start
#!/usr/bin/env bash

unset a b c
printf $'\nExplicit declarations statements:\n'
printf $'\ntypeset -i a=2 b=$a c="$((a - 1))":\n=> '
typeset -i a=2 b=$a c="$((a - 1))"
printf 'a=%d b=%d c=%d\n' "${a}" "${b}" "${c}"
unset a b c
printf $'\ndeclare a=hello b=world c="$a $b":\n=> '
declare a='hello' b='world' c="${a} ${b}"
printf $"a='%s' b='%s' c='%s'\\n" "${a}" "${b}" "${c}"

unset a b c
printf $'\nImplicit declarations statements:\n'
a=2 b=$a c="$((a - 1))"
printf $'\na=2 b=$a c="$((a - 1))":\n=> '
printf 'a=%d b=%d c=%d\n' "${a}" "${b}" "${c}"
unset a b c
a='hello' b='world' c="${a} ${b}"
printf $'\na=hello b=world c="$a $b":\n=> '
printf $"a='%s' b='%s' c='%s'\\n" "$a" "$b" "$c"
==== knip code end

Output:
> Explicit declarations statements:
>
> typeset -i a=2 b=$a c="$((a - 1))":
> => a=2 b=2 c=1
>
> declare a=hello b=world c="$a $b":
> => ./b.sh[10]: declare: not found [Aucun fichier ou dossier de ce type]
> a='' b='' c=''
>
> Implicit declarations statements:
>
> a=2 b=$a c="$((a - 1))":
> => a=2 b=2 c=1
>
> a=hello b=world c="$a $b":
> => a='hello' b='world' c='hello world'

ksh93 resolves explicit back-references with typeset.

--
Léa Gris

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