TIP #471: ADD [INFO LINKEDNAME] INTROSPECTION COMMAND 
=======================================================
 Version:      $Revision: 1.1 $
 Author:       Mathieu Lafon <mlafon_at_gmail.com>
 State:        Draft
 Type:         Project
 Tcl-Version:  8.7
 Vote:         Pending
 Created:      Friday, 05 May 2017
 URL:          https://tip.tcl-lang.org471.html
 Post-History: 

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 ABSTRACT 
==========

 This TIP proposes to improve link variable introspection by providing a 
 new *info linkedname* command. 

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

 This TIP is related to discussions about [TIP #457] and the *-upvar* 
 extended argument specifier. Adding an intropsection command to get the 
 name of the variable linked to is more Tcl-ish than automatically 
 adding a local variable with the linked name. The proposed command is 
 not restricted to [TIP #457] usage as this can also be used for a link 
 variable created by other means, using the *upvar* command for example. 

 SPECIFICATION OF THE PROPOSED CHANGE 
======================================

 There should be a new subcommand of *info* created with the following 
 syntax: 

       *info linkedname* /varname/ 

 The /varname/ should be the name of a variable that has been linked to 
 another variable (e.g., with *upvar*, *global*, *variable* or 
 *namespace upvar*), and the result of the command will be the name of 
 the variable linked to. 

 REFERENCE IMPLEMENTATION 
==========================

 The reference implementation is available in the info-linkedname 
 [<URL:http://core.tcl.tk/tcl/timeline?r=info-linkedname>] branch. 

 The code is licensed under the BSD license. 

 IMPLEMENTATION NOTES 
----------------------

 Depending on the linked variable, the name is found using different 
 methods: 

     * The name of a variable present in a hash table (globals, local 
       variables created at runtime, ...) is retrieved using the hash 
       key; 

     * The name of an array element is built using the name of the array 
       and the index name, retrieved using the hash key. A new field is 
       added to the TclVarHashTable sructure to access the related array 
       variable from the array element; 

     * The name of a compiled local variable is searched in current or 
       upper call frames. 

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

 This document has been placed in the public domain. 

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