TIP:            186
Title:          Expose the Type and Modified-State of Widget Options
Version:        $Revision: 1.4 $
Author:         Peter MacDonald <pmacdona@pdqi.com>
Author:         Peter MacDonald <peter@pdqi.com>
State:          Draft
Type:           Project
Vote:           Pending
Created:        16-Apr-2004
Post-History:   
Keywords:       Tk
Tcl-Version:    8.7

~ Abstract

This TIP adds a 6th (and 7th element) to each option in the output of
[[''path'' '''configure''']] for Tk widgets, indicating the type and
modified status of each option respectively.

~ Rationale

The configure subcommand of Tk widgets provides a powerful method for
introspection of widget state information.  Unfortunately, two
important pieces of information are currently unavailable.  Namely,
the type Tk is expecting for an option and the whether a user has
explicitly assigned a value.

The type field is valuable in automating interfaces for editing the
contents of widgets.

The modified field is useful in changing styles (such as in
'''tk_setPalette''') where we update all widgets that are currently
using default values.

~ Specification

The configure subcommand for Tk widgets, when invoked with no
arguments, currently dumps out all options as a list with 5 elements
per-option: optName, dbName, dbClass, defValue, optValue.  This TIP
proposes adding up to 2 additional values: '''optType''' and
'''optModified'''.

 * A 6th element, '''optType''', is a string representation of the
   type field of '''Tk_ConfigSpec''' and '''Tk_OptionSpec'''.

 * For widgets using the new '''Tk_OptionSpec''', a 7th appended
   element indicates whether an option has been set by the user.

~ Notes

Perhaps '''optModified''' should be specified as an enumeration.  For
example:

  * 1 = '''USER_MODIFIED'''

  * 2 = '''OPTION_DATABASE'''

  * 3 = '''SYSTEM_DEFAULT'''

  * 4 = '''TABLE_DEFAULT'''

In addition, as much of the Tk core is still using
'''Tk_ConfigSpec''', would some form of compatibility interface make
sense whereby a '''Tk_ConfigSpec''' could be used to dynamically
produce a '''Tk_OptionSpec'''?  (This last is out of the scope of this
TIP.)

Probably also need a way to change options such that the '''USER_MODIFIED''' flag does not get set. (eg. '''tk_setPalette''')

~ Changes

Threre are a couple of small changes to ''tkConfig.c'' and
''tkOldConfig.c'', plus a #define of '''TK_OPTION_VALUE_SET''' in
''tk.h''

~ Overhead/Impact

Scripts currently exploiting introspection and depending upon a list
length of 5 may break.

~ Reference Implementation

There is a simple implementation of the above available as a patch
against Tk 8.4.2[http://pdqi.com/configure.diff.gz].  It does not
implement a enumerated flag for '''optModified''', and the type string
lookup is rather crude.

~ Copyright

This document has been placed in the public domain.