Re: declare [-+]n behavior on existing (chained) namerefs

[Piotr Grzybowski]

 this one does not seem like a bug to me, rather a decision made by the author: 
to interpret "on the variable" from this:

"All references, assignments, and attribute modifications to name, except for 
changing the -n attribute itself, are performed on the variable referenced by 
name’s value."

as doing a depth first search (going as deep as possible over the reference 
chain) in order to find the variable. The last case you mention is discussable: 
when the leaf is an empty reference should +n do something? Probably should do 
the same as declare +n ref_N; which I think is just to leave a variable with 
identifier ref_N. But then, ref_((N-1)) points to a variable and suddenly there 
is a potentially unexpected change in your lovely tree of empty references.
 One can argue: if you pass the ref_i to some function, and you want to modify 
ref_N how to do it? The choice made seems fairy logical, I am not saying that 
it is the best possible one though.

cheers,
pg



On 27 Apr 2016, at 21:26, Grisha Levit wrote:

> declare -n name=value, when name is already a nameref, shows the following 
> presumably inconsistent behavior:
> 
> Given a chain of namerefs like:
> 
> ref_1 -> ref_2 -> ... -> ref_i ... -> ref_N [-> var]
> 
>       • If ref_N points to a name that is not a nameref, the operations 
> declare -n ref_N=value and declare +n ref_N modify the value/attributes of 
> ref_N (this seems to be the desired behavior)
>       • For i<N, declare -n ref_i=value and declare +n ref_i modify the 
> value/attributes of ref_N and not of ref_i
>       • If ref_N is declared as a nameref but unset, then these operations on 
> ref_i have no effect.
> For example, starting with:
> 
> unset -n ref{1..3
> }
> 
> declare
>  -n ref1=ref2 ref2=ref3 ref3=var1
> 
> # declare -n ref1=var2
> # declare -p ref{1..4}
> declare -n ref1="ref2"   # unchanged
> declare -n ref2="ref3"
> declare -n ref3="var2"   # changed
> # declare +n ref1
> # declare -p ref{1..3}
> declare -n ref1="ref2"   # unchanged
> declare -n ref2="ref3"
> declare -- ref3="var1"   # changed, no loner nameref
> Or alternatively:
> 
> unset -n ref{1..3
> }
> 
> declare
>  -n ref1=ref2 ref2=ref3 ref3
> 
> # declare +n ref1
> # declare -p ref{1..3}
> declare -n ref1="ref2"   # unchanged
> declare -n ref2="ref3"   # unchanged
> declare -n ref3          # unchanged
> # declare -n ref1=var1
> # declare -p ref{1..3}
> declare -n ref1="ref2"
> declare -n ref2="ref3"
> declare
>  -n ref3
> 
> The man page says:
> 
> All references, assignments, and attribute modifications to name, except for 
> changing the -n attribute itself, are performed on the variable referenced by 
> name’s value.
> 
> This does not appear to be the case, as declare -n ref_N=value changes 
> $ref_N, not $value, and declare +n ref_i changes ref_N.
>