Re: Incorrect / Inconsistent behavior with nameref assignments in functions

[Oğuz]

28 Ağustos 2020 Cuma tarihinde Binarus <lists@binarus.de> yazdı:

>
>
> On 28.08.2020 17:37, Oğuz wrote:
> > 28 Ağustos 2020 Cuma tarihinde Greg Wooledge <wooledg@eeg.ccf.org>
> yazdı:
> >
> >> On Fri, Aug 28, 2020 at 10:56:34AM +0200, Binarus wrote:
> >>> #!/bin/bash
> >>>
> >>> function Dummy() {
> >>>
> >>>   local -n namerefArray="$1"
> >>>   local -a -i myArray=("${namerefArray[@]}")
> >>>
> >>>   local -p
> >>> }
> >>>
> >>> declare -a -i myArray=('1' '2' '3')
> >>
> >> You've got a local variable with the same name as the global variable
> >> that you're attempting to pass by reference.  This will not work.
> >>
> >>
> > These scripts yield identical output on bash-5.1 though.
>
> Thank you very much for testing! This is interesting. I couldn't get my
> hands on a system with 5.1 yet.
>
>
5.1 is still in beta phase.


> With 5.1, do both scripts behave like SCRIPT 1 with the older versions
> or like SCRIPT 2 with the older versions?


They behave like SCRIPT 2 as expected, local `myArray' is populated with
the contents of global `myArray'. _identical_ was the wrong word though,
the second script doesn't copy the integer attribute.


> >> Namerefs (declare -n) in bash are *not* like uplevel commands in Tcl.
> >> They cause the referenced variable name to be evaluated just like any
> >> other variable would be, starting at the current function scope, then
> >> going up to the caller, and so on.
> >>
> >> If you want to use namerefs in a function in bash, you MUST go out of
> >> your way to minimize the chances of a collision between the caller's
> >> variable refererance and ANY local variable of the function.  Not just
> >> the nameref itself, but any other incidental variables used in the
> >> function.  (As you aptly demonstrated here.)
> >>
> >> So, you can't write functions like this:
> >>
> >> func1() {
> >>   declare -n ref="$1"
> >>   local i
> >>   ...
> >> }
> >>
> >> Instead, you need crazy things like this:
> >>
> >> func1() {
> >>   declare -n _func1_ref="$1"
> >>   local _func1_i
> >>   ...
> >> }
> >>
> >>
> > This doesn't make the slightest sense. What is the point of having local
> > variables then?
>
> Or namerefs ... I totally agree. Either locals or namerefs are just
> unusable given that situation; you have to choose between them.
>
> Thank you very much, and best regards,
>
> Binarus
>
>

-- 
Oğuz