From: Hidetoshi NAGAI <nagai@...>
Date: 2005-07-15T14:46:01+09:00
Subject: Re: Perl/Tk, CheckButtons, and modifying variables

From: "David Douthitt" <ssrat@mailbag.com>
Subject: Re: Perl/Tk, CheckButtons, and modifying variables
Date: Fri, 15 Jul 2005 08:15:51 +0900
Message-ID: <1121382859.564956.239480@g44g2000cwa.googlegroups.com>
> I didn't see anything in "The Ruby Way" and I didn't have my PickAxe
> book with me.  The PerlTk documents don't have a "Variable" or a
> "TkVariable" listed anywhere.

Ruby/Tk accesses to Tcl's variables through TkVariable objects.

# Of course, "wait" and "trace" are available like as a Tcl's variable.

As you know, each value is kept as a string on a Tcl/Tk interpreter.
So, a Ruby's object which set to a Tcl's variable is converted to a 
string (with TkUtil._get_eval_string() and so on).

Usually, use TkVariable#value/value= when the Tcl's variable is a
scalar type, or use TkVariable#[]/[]= when the variable is an array.
TkVariable.new creates a scalar variable. 
However, TkVariable.new(<Hash object>) or TkVariable.new_hash creates 
an array variable. For example, 
-----------------------------------
v = TkVariable.new
v['a'] = 1    #=> raise exception!!
-----------------------------------
-----------------------------------
v = TkVariable.new(Hash.new)
v['a'] = 1
v['a']        #=> "1"
v.value       #=> {"a"=>"1"}
-----------------------------------

The following is based on the latest version of Ruby/Tk.

To help to access the value of Tcl's variable, TkVariable has some 
kind of access methods.
-------------------------------------------------
 -----------+-----------+-----------
   type     |  get      |  set
 ===========+===========+===========
  String    | value     | value=
 -----------+-----------+-----------
  Symbol    | symbol    | symbol=
 -----------+-----------+-----------
  Numeric   | numeric   | numeric=
 -----------+-----------+-----------
  Boolean   | bool      | bool=
 -----------+-----------+-----------
  List      | list      | list=
 -----------+-----------+-----------
  Num-List  | numlist   | numlist=
 -----------+-----------+-----------
  Variable  | variable  | variable=
 -----------+-----------+-----------
  Widget    | window    | window=
 -----------+-----------+-----------
  Procedure | procedure | procedure=
 -----------+-----------+-----------

 * 'List' means that is a list of strings, and 'Num-List' means that 
   is a list of Numeric values.

 * 'Variable' means that its value is a Tcl's variable name. 
   TkVariable#variable returns a TkVariable object.

 * 'Widget' means that its value is a widget path. 
   TkVariable#window returns a widget object.

 * 'Procedure' means that its value is a script. 
   If set a proc object to the variable, TkVariable#procedure returns 
   a proc object.
-------------------------------------------------
Based on that, 
-----------------------------------
v = TkVariable.new('no')
v.value       #=> 'no'
v.bool        #=> false
-----------------------------------
-----------------------------------
v = TkVariable.new(1)
v.numeric += 2
v.value        #=> "3"
-----------------------------------

TkVariable object can have 'TYPE' of its value.
Default TYPE is nil. Then, TkVariable#value returns a string.
-----------------------------------
v = TkVariable.new(1)
v.default_value_type  #=> nil
v.value        #=> "1"
-----------------------------------
When set the TYPE, TkVariable#value returns a value of the TYPE.
-----------------------------------
v = TkVariable.new(1)
v.default_value_type = :numeric
v.value        #=> 1
-----------------------------------

TkVariable has some operator methods.
For example, 
-----------------------------------
v = TkVariable.new(1)
v + 2   #=> 3
-----------------------------------
-----------------------------------
v = TkVariable.new('asdf')
v + 'qwer'   #=> 'asdfqwer'
-----------------------------------

Please see tk/variable.rb for other methods and ask if you have some 
questions. 
-- 
Hidetoshi NAGAI (nagai@ai.kyutech.ac.jp)