Re: Passing variables by reference conflicts with local

[Dennis Williamson]

Wouldn't you want your name collision test before your call to the
private function - just to save the wasted call? (And to have its
message redirected to stderr and have a "return 1" or other non-zero
value?) Otherwise, I think your idea is a good one, especially if the
public function can be as simple as that.

Thanks, Pierre, by the way, for the workarounds. I hadn't considered
using indirection that way.

On Sat, May 1, 2010 at 6:21 AM, Freddy Vulto <fvulto@gmail.com> wrote:
> On 100501 12:40, Pierre Gaston wrote:
>> On Sat, May 1, 2010 at 12:26 PM, Dennis Williamson wrote:
>> > As Chet said, use internal variables that are unlikely to conflict.
>> You can use workarounds like:
>> printf -v $a "%s" foobar
>> read $a <<< "%s"
>
> The problem with obfucscated internal variables I think is that my
> library code becomes unnecessary obfuscated.  That's why I'm thinking an
> additional call-layer (workaround 2 in my original mail) is an
> improvement in that the private library code "_blackbox()" can use
> simple, readable variables without restrictions/conflicts, while the
> public layer "blackbox()" checks conflicts, which - unlikely as they
> might be - I'd like to return to my library users as a known error
> instead of silent failing.
>
> Revised example, replacing eval with printf -v, thanks:
>
>    # Param: $1  variable name to return value to
>    # Private library function. Do not call directly. See blackbox()
>    _blackbox() {
>        # Just don't declare "local __1"
>        local a b c d e f g h i j
>        # ...
>        # Lots of complicated library code here
>        # ...
>        # Return value
>        printf -v $1 %s b
>    }
>
>    # Param: $1  variable name to return value to
>    # Public library function
>    blackbox() {
>        local __1
>        _blackbox __1
>        [[ $1 == __1 ]] && echo "ERROR: variable name conflicts"\
>                "with local variable: $1"
>        printf -v $1 %s "$__1"
>    }
>
>    blackbox a; echo $a           # Outputs "b" all right
>    blackbox __1                  # Outputs error
>    d='ls /;true'; blackbox "$d"  # No more oops
>
>
> Freddy Vulto
> http://fvue.nl/wiki/Bash:_passing_variables_by_reference
>
>
>