Is this a bug?

I was using the tcllib::dns package and
couldn't get it to load. I traced the
problem down to this small example which
results in the error message
"Couldn't save command result in variable"

set msg(1) one ;# Turn msg into an array
namespace eval ::foo {
catch {package require notFound} msg
}

It appears the global msg and the ::foo msg
variables are getting .

It's easy to work around the bug--just fully
qualify the second msg--but this appears in
tcllib code.

Keith

keithv wrote:
> I was using the tcllib::dns package and
> couldn't get it to load. I traced the
> problem down to this small example which
> results in the error message
>  "Couldn't save command result in variable"
>
>   set msg(1) one ;# Turn msg into an array
>   namespace eval ::foo {
>     catch {package require notFound} msg
>   }
>
> It appears the global msg and the ::foo msg
> variables are getting .
>
> It's easy to work around the bug--just fully
> qualify the second msg--but this appears in
> tcllib code.

The really safe solution is to add the line

variable msg

right before the 'catch ...', within the 'namespace eval ::foo' block.

Sadly, that is the way Tcl's variable resolution is specified: if a
variable is not found in the current namespace, it is looked up as a
global variable. If a global is found, it is used. Otherwise a variable
in the current namespace is created. Nasty, IMO. We will not be able to
fix this in the short run :(

So, the rule is: if you want to make sure that you are using a variable
in the current namespace, do "declare" it with [variable].

Miguel

keithv wrote:
> I was using the tcllib::dns package and
> couldn't get it to load. I traced the
> problem down to this small example which
> results in the error message
>  "Couldn't save command result in variable"
>
>   set msg(1) one ;# Turn msg into an array
>   namespace eval ::foo {
>     catch {package require notFound} msg
>   }

If you want namespace restricted resolution of a variable name,
use [variable] to set it up:

set msg(1) one ;# Turn msg into an array
namespace eval ::foo {
variable msg
catch {package require notFound} msg ;# Now this means ::foo::msg
}

Tcl prefers to resolve a variable name to any existing variable rather
than create a new one.

--
| Don Porter          Mathematical and Computational Sciences Division |
| donald.porter@nist.gov             Information Technology Laboratory |
| http://math.nist.gov/~DPorter/                                  NIST |
 |_______________________________________
_______________________________|

"keithv" <kvetter@gmail.com>,
In a message on 27 Apr 2005 12:37:32 -0700, wrote :

"> I was using the tcllib::dns package and
"> couldn't get it to load. I traced the
"> problem down to this small example which
"> results in the error message
">  "Couldn't save command result in variable"
">
">   set msg(1) one ;# Turn msg into an array
">   namespace eval ::foo {
">     catch {package require notFound} msg
">   }
">
"> It appears the global msg and the ::foo msg
"> variables are getting .

Nope.  You did not declare the msg in the namespace to be a variable.
It is still the global msg and you are trying to set a scalar value in a
variable that was bound to an array.

">
"> It's easy to work around the bug--just fully
"> qualify the second msg--but this appears in
"> tcllib code.

Might be a bug in the tcllib or maybe something else.

">
"> Keith
">
">

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