TIP #184: AVOID CREATING UNUSABLE VARIABLES 
=============================================
 Version:      $Revision: 1.4 $
 Author:       Miguel Sofer <msofer_at_users.sf.net>
 State:        Final
 Type:         Project
 Tcl-Version:  8.5
 Vote:         Done
 Created:      Saturday, 27 March 2004
 URL:          https://tip.tcl-lang.org184.html
 Post-History: 

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 ABSTRACT 
==========

 Both *upvar* and *global* can create unreachable variables: scalar 
 variables whose name looks like an array element, e.g., a(b). This 
 behaviour is documented in the *upvar* manpage. This TIP proposes that 
 both *upvar* and *global* raise errors instead of creating such 
 variables. 

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

 As detailed in [Bug #600812] 
 [<URL:http://sf.net/tracker/?func=detail&aid=600812&group_id=10894&atid=110894>], 
 both *upvar* and *global* can create unreachable variables: scalar 
 variables whose names looks like an array element. 

 One example is: 

      upvar 0 x(1) y(1)

 which creates a /scalar/ variable named y(1) that is linked to the 
 element 1 of the array x. However, there is no way for a tcl script to 
 read or write such scalar variables, the parser will interpret that 
 name as referring to an element of the array named y. 

 Another example is: 

      proc a {} {
          global x(1)
          ...
      }

 which will create a scalar local variable named 'x(1)', linked to the 
 element 1 of theglobal array x. Again, this variable is unreachable. 

 This TIP proposes *upvar* and *global* raise an error rather than 
 creating such a variable, mimicking in this respect the behaviour of 
 *variable*. 

 Note that a TIP is required because the behaviour of *upvar* is 
 documented in the manual page, so that it cannot really be described as 
 a bug: 

       MyVar is always treated as the name of a variable, not an array 
       element. Even if the name looks like an array element, such as 
       a(b), a regular variable is created. 

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

 There is a patch attached to the bug ticket 
 [<URL:http://sf.net/tracker/?func=detail&aid=600812&group_id=10894&atid=110894>] 
 that implements this TIP. 

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

 This TIP is in the public domain. 

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