Re: ${var@A}; hypothetical, related parameter transformations

[Chet Ramey]

On 3/20/24 3:05 PM, Zachary Santer wrote:

> > That expansion will produce a declare command if the variable has any
> > attributes, since it needs one to reproduce them. If the variable has a
> > value, but no attributes, you'll get an assignment  statement. If there
> > are no attributes and no value, you get nothing.
>
> I hadn't even considered what to do with a variable that's declared,
> but without attributes or value.

It really only matters when you use declare in a function, where the
resultant unset variable will be local when its assigned a value.

> Let's say we've got two variables defined in a function like so:
>
> func () {
>    local -ir number=12
>    local color='turquoise;
>    local number_message
>    generate_declare_command number number_message
>    local color_message
>    generate_declare_command color color_message
> }

One of the changes I'm proposing here is to have ${color_message@A}
generate a declare command (`declare color_message'). It's an omission
that it wasn't there before, and a problem that the expansion was null.
Look at all the work you have to do to compensate.


> it's more work
> than if there were three separate parameter transformations. one each
> to always generate a declare command; an assignment statement; and the
> right hand side of a compound assignment statement or standard
> assignment statement, depending on whether it's dealing with an
> array/assoc or scalar.

I am not convinced that tripling the number of relevant variable
transformations makes the problem any simpler.

> Consider that you're talking about changing ${var@A} to expand to a
> declare command in the case that the variable has no attributes but is
> local to the scope in which the expansion occurs. If you make that
> change, then ${var@A} is somewhat unpredictable if you can't assume a
> given bash release.

It's semantically wrong otherwise. A simple assignment statement would
create a global variable if the name weren't separately declared local.
That is "recreating the variable" by some definition, but if your goal
is to save a variable, unset it, and then restore it at the same scope,
it doesn't work. Dynamic scoping and using these expansions on a variable
that's declared as local in a previous scope gets messy, of course.

--
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    chet@case.edu    http://tiswww.cwru.edu/~chet/

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