TIP #140: TRACING NAMESPACE MODIFICATIONS 
===========================================
 Version:      $Revision: 1.2 $
 Author:       Donal K. Fellows <donal.k.fellows_at_man.ac.uk>
 State:        Deferred
 Type:         Project
 Tcl-Version:  8.5
 Vote:         Pending
 Created:      Wednesday, 04 June 2003
 URL:          https://tip.tcl-lang.org140.html
 Post-History: 

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 ABSTRACT 
==========

 This TIP allows scripts to register callbacks to monitor alterations to 
 namespaces, such as their deletion, the creation, renaming and deletion 
 of commands within the namespace and modifications to the exports list 
 of the namespace. 

 RATIONALE 
===========

 As part of my work on an experimental [TIP #112] implementation, I have 
 discovered that computing the list of public (i.e. exported) commands 
 from a namespace is a comparatively expensive operation. This means 
 that it is necessary (well, highly desirable) to cache the list of 
 exports from a namespace. But then I thought that it might be nice to 
 expose that interface to use to better enable namespaces to support 
 other interesting uses, and that it should be possible to implement the 
 default behaviour in a Tcl script. It is in support of this that I 
 present this TIP; I also add the ability to trace deletion of the 
 namespace as a fairly obvious extension. 

 PROPOSED CHANGE AT TCL SCRIPT LEVEL 
=====================================

 I propose that the [trace] command be extended with a new type of thing 
 to trace: a namespace. The operations that would trigger a trace are: 

     * Namespace deletion (subject to the same sorts of restrictions in 
       relation to deleted interpreters that are present for traces of 
       command deletion) with the ops value /delete/. 

     * Command list modification (being creation, renaming or deletion 
       of any command within that namespace) with the ops value 
       /command/. Modification due to deletion of the namespace will not 
       trigger traces with this operation, but instead the /delete/ 
       operation outlined above (subject to the caveats relating to 
       interpreter deletion.) 

     * Exports list modification (i.e. updates with [namespace export]) 
       with the ops value /export/. Modification due to the deletion of 
       the namespace will not trigger this traces with this operation, 
       but instead the /delete/ operation outlined above (subject to the 
       caveats relating to interpreter deletion.) 

 In each case, the trace callback script will have the fully qualified 
 name of the namespace and the name of the triggering operation appended 
 to it before execution. In the case of command list modification by the 
 /creation/ of a command (which might also be through import of commands 
 from another namespace, for example) there will be an extra parameter 
 being the /local/ name of the command (without namespace separators.) 

 These changes will be propagated to each of the [trace add], [trace 
 remove] and [trace info] subcommands, of course. 

 PROPOSED CHANGE AT C API LEVEL 
================================

 Yet to be designed, but will be based as closely as possible on the 
 existing Tcl trace APIs. 

 COPYRIGHT 
===========

 This document has been placed in the public domain. 

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