Re: V+=1 doesn't work if V is a reference to an integer array element

[Léa Gris]

Le 13/01/2021 à 22:13, Chet Ramey écrivait :
> The `-i' forces arithmetic evaluation, which makes this expand to the 
> equivalent of `declare -n b=1'. That's an invalid name for a nameref,
> which you'd see if you used `declare -n b=1' instead. The assignment
> error causes `declare' to return an non-zero status, but the error
> message checks the original value, not the result of arithmetic
> evaluation, and the `a[0]' is valid.
>
> I guess I never thought people would try to use integer variables as
> namerefs, since nameref values can't be digits.


Sorry Chet, this does not make sense to me. There is no error message.
It look like to replied about Greg's post.

I still wonder how when performing b+=number, the referenced value of 
a[0] is multiplied by 2 and the added the number back to a[0]

If a[0] is 4 and you do b+=2, then a[0] would be updated to 10

The integer attribute to the nameref variable just make it work in 
arithmetic assignation var+=value without causing an error.

I don't understand why this exact sequence:

unset a; unset -n b; \
declare -ai a=('4'); \
declare -n b='a[0]'; \
typeset -ni b; \
declare -p a b; \
b+=2; \
declare -p a b

Produces this output of the a array:

declare -ai a=([0]="4")
declare -in b="a[0]"
declare -ai a=([0]="10")
declare -in b="a[0]"

I set the integer attribute to the nameref b after it has been assigned 
the "a[0]" string, so it keeps its string nameref value but is now also 
considered as an integer value.


--
Léa Gris