Namespace context missing in trace variable

[tombert]

Hi All,

I was trying to trace a NS (origin) variable from another NS (testns). But when the CommandPrefix procedure is triggered, it is without the NS context - Instead of "origin::myvar1" it gets "myvar1" only.

The manual says: "CommandPrefix executes in the same context as the code that invoked the traced operation" but simply adding a "variable $name" inside the CommandPrefix "proc global" does not help.

A workaround would be adding some custom command parameters to the "CommandPrefix" but I was hoping for a better explanation if I am doing something wrong.


Regards
Thomas


namespace eval origin {
namespace ensemble create
namespace export set
variable myvar1 0

proc set args {
foreach {name value} $args {
variable $name
::set $name $value
}
}
}

namespace eval testns {
namespace ensemble create
namespace export register

namespace eval register {
namespace ensemble create
namespace export global

proc global {args} {
foreach name $args {
uplevel #0 [list trace add variable $name write [list testns::sync::global]]
}
}
}

namespace eval sync {
namespace ensemble create
namespace export global

proc global {name index op} {
## where is the context!?
## error: can't read "myvar1": no such variable
puts "'$name' was changed to '[set $name]'"
}
}
}

testns register global origin::myvar1
origin set myvar1 something

[Don Porter]

On 06/22/2015 05:54 AM, tombert wrote:
> Hi All,
>
> I was trying to trace a NS (origin) variable from another NS (testns). But when the CommandPrefix procedure is triggered, it is without the NS context - Instead of "origin::myvar1" it gets "myvar1" only.
>
> The manual says: "CommandPrefix executes in the same context as the code that invoked the traced operation" but simply adding a "variable $name" inside the CommandPrefix "proc global" does not help.
>
> A workaround would be adding some custom command parameters to the "CommandPrefix" but I was hoping for a better explanation if I am doing something wrong.

Quick answer: you need to use [upvar].

--
| Don Porter Applied and Computational Mathematics Division |
| donald...@nist.gov Information Technology Laboratory |
| http://math.nist.gov/~DPorter/ NIST |
|______________________________________________________________________|

[tombert]

On Wednesday, 24 June 2015 15:29:08 UTC+2, Don Porter wrote:
> On 06/22/2015 05:54 AM, tombert wrote:
> > Hi All,
> >
> > I was trying to trace a NS (origin) variable from another NS (testns). But when the CommandPrefix procedure is triggered, it is without the NS context - Instead of "origin::myvar1" it gets "myvar1" only.
> >
> > The manual says: "CommandPrefix executes in the same context as the code that invoked the traced operation" but simply adding a "variable $name" inside the CommandPrefix "proc global" does not help.
> >
> > A workaround would be adding some custom command parameters to the "CommandPrefix" but I was hoping for a better explanation if I am doing something wrong.
>
> Quick answer: you need to use [upvar].
>
> --
> | Don Porter Applied and Computational Mathematics Division |

> | donald dot porter et nist.gov Information Technology Laboratory |
> | http://math.nist.gov/~DPorter/ NIST |
> |______________________________________________________________________|

thx, this helped a little bit. Still I do not get the context. I tried using uplevel, then call [namespace current] but it returns the context of "testns::sync". Wheras I expect it to be "origin".

proc global {name index op} {

uplevel 1 [list
puts [namespace current] ;# returns wrong context
puts "'$name' was changed to '[set $name]'" ;# error no such variable
]
}



And I tried [upvar]. Here I can read the correct value of "myvar". But the request to [namespace which -variable myvar] results in an empty string.

proc global {name index op} {

upvar $name myvar
puts [namespace which -variable myvar] ;# returns an emtpy string
puts "'$name' was changed to '[set $name]'" ;# returns correct value
}


When reading the manual "CommandPrefix executes in the same context as the code that invoked the traced operation" I would expect either [uplevel] or [upvar] together with [namespace current] or [namespace which -variable] to get the actual context returned.


thx

[Don Porter]

On 06/24/2015 10:54 AM, tombert wrote:

>>> The manual says: "CommandPrefix executes in the same context as the code that invoked the traced operation" but simply adding a "variable $name" inside the CommandPrefix "proc global" does not help.

Don Porter wrote:
>> Quick answer: you need to use [upvar].

On 06/24/2015 10:54 AM, tombert wrote:>
> proc global {name index op} {
> uplevel 1 [list
> puts [namespace current] ;# returns wrong context
> puts "'$name' was changed to '[set $name]'" ;# error no such variable
> ]
> }

That's not a proper use of [uplevel]. Apply Tcl substitution rules to
see that [namespace current] is evaluated locally.

> proc global {name index op} {
> upvar $name myvar
> puts [namespace which -variable myvar] ;# returns an emtpy string
> puts "'$name' was changed to '[set $name]'" ;# returns correct value
> }

What you want is

proc global {name index op} {

upvar 1 $name myvar
puts [uplevel 1 [list ::namespace which -variable $name]]
puts "'$name' was changed to '$myvar'"

}

--
| Don Porter Applied and Computational Mathematics Division |

| donald...@nist.gov Information Technology Laboratory |
| http://math.nist.gov/~DPorter/ NIST |
|______________________________________________________________________|

[tombert]

thx for your support. got it now.