[Xotcl] why Attribute is not imported?

Stefan Sobernig stefan.sobernig at wu.ac.at
Mon Nov 2 09:29:10 CET 2009


> XOTcl 1.6.4, works ok from xotclsh and when 'namespace import ::xotcl::*' 
> comes right after 'package require XOTcl' and not within test1 namespace.

This behaviour is due to an interaction between the implementation 
strategy for slots as implemented in XOTcl 1.5+ and the standard 
namespace/command resolution rules of Tcl.

(::xotcl::)Attribute is declared and resolved for the scope of a 
per-object namespace ::test1::Test::slot. This namespace is acquired 
upon calls to the slot method of ::xotcl::Class. You may find out by 
inspecting the return value of [namespace current] (see below). While 
this is merely an implementation detail and should not concern the XOTcl 
developer, it interferes with the way Tcl resolves relatively-qualified 
command (and variable) names. While slightly more complex at second 
sight, generally speaking, the command name (e.g., Attribute) is first 
searched for in the current ns (::test1::Test::slot) and then in the 
global one (::):

see Section "NAME RESOLUTION" at 

Intermittent ones are skipped (e.g., ::test1, ::test1::Test). Hence the 
behaviour you are observing. This also explains why a [namespace import 
::xotcl::*] in the /global/ ns (e.g., following [package req XOTcl]) is 
a valid fix.

You may also consider:

1. fully-qualified command names: ::xotcl::Attribute
2. a preceding [namespace import ::xotcl::*] in the '-slots' block (see 
3. use of [namespace path] starting with 8.5 (see below)


package provide test1 0.1
package require XOTcl

# ::test1
namespace eval ::test1 {
   # [namespace current] -> ::test1
   namespace import ::xotcl::*
   # alternatively: namespace path ::xotcl
   Class ::test1::Test -slots {
     # [namespace current] -> ::test1::Test::slot
     namespace import ::xotcl::*
     # alternatively: namespace path ::xotcl
     Attribute name
   namespace export Test
namespace import ::test1::*


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