From: Morton Goldberg <m_goldberg@...>
Date: 2007-04-09T15:38:02+09:00
Subject: Re: Can a TkVariable store a symbol?

On Apr 8, 2007, at 10:24 PM, Hidetoshi NAGAI wrote:

> From: Alex DeCaria <alex.decaria@millersville.edu>
> Subject: Re: Can a TkVariable store a symbol?
> Date: Mon, 9 Apr 2007 08:26:33 +0900
> Message-ID: <dd2b9ec33344b0790a73d090f4b02785@ruby-forum.com>
>> Thanks Morton - That's what I needed to know.
>
> TkVariable can convert Tcl's string to Ruby's object automatically.
> If you want to treat a Symbol on a TkVariable,
> you can set 'default_value_type' of the TkVariable object.
> For example,
> -------------------------------------------------------------
> $ irb
> irb(main):001:0> require 'tk'
> => true
> irb(main):002:0> a = TkVariable.new
> => #<TkVariable: v00000>
> irb(main):003:0> a.value = :hi
> => :hi
> irb(main):004:0> a.value
> => "hi"
> irb(main):005:0> a.symbol
> => :hi
> irb(main):006:0> b = TkVariable.new(:hi, :symbol)
> => #<TkVariable: v00001>
> irb(main):007:0> b.value
> => :hi
> irb(main):008:0> b.string
> => "hi"
> irb(main):009:0> a.default_value_type
> => nil
> irb(main):010:0> b.default_value_type
> => :symbol
> irb(main):011:0> a.numeric
> ArgumentError: invalid value for Number: 'hi'
>         from /usr/local/lib/ruby/1.8/tk/variable.rb:706:in `number'
>         from /usr/local/lib/ruby/1.8/tk/variable.rb:706:in `numeric'
>         from (irb):20
>         from :0
> irb(main):012:0> a.default_value_type = :symbol
> => :symbol
> irb(main):013:0> a.value
> => :hi
> irb(main):014:0> b.default_value_type = :string
> => :string
> irb(main):015:0> b.value
> => "hi"
> irb(main):016:0> a.value = 3
> => 3
> irb(main):017:0> a.value
> => :"3"
> irb(main):018:0> a.numeric
> => 3
> irb(main):019:0> a.symbol
> => :"3"
> irb(main):020:0> a.list
> => ["3"]
> irb(main):021:0> a.numlist
> => [3]
> irb(main):022:0> a.bool
> => true
> irb(main):023:0> a.value = 1
> => 1
> irb(main):024:0> a.bool
> => true
> irb(main):025:0> a.value = 0
> => 0
> irb(main):026:0> a.bool
> => false
> irb(main):027:0> a.value = 'yes'
> => "yes"
> irb(main):028:0> a.bool
> => true
> irb(main):029:0> a.value = 'no'
> => "no"
> irb(main):030:0> a.bool
> => false
> irb(main):031:0> a.value = true
> => true
> irb(main):032:0> a.bool
> => true
> irb(main):033:0> a.value = false
> => false
> irb(main):034:0> a.bool
> => false
> irb(main):035:0> a.value
> => :"0"
> irb(main):036:0> a.string
> => "0"
> irb(main):037:0> a.value = true
> => true
> irb(main):038:0> a.string
> => "1"
> irb(main):039:0>
> -------------------------------------------------------------
>
> And, following operations are available too.
>
> -------------------------------------------------------------
> $ irb
> irb(main):001:0> require 'tk'
> => true
> irb(main):002:0> a = TkVariable.new(1)
> => #<TkVariable: v00000>
> irb(main):003:0> a.value
> => "1"
> irb(main):004:0> a + 1
> => 2
> irb(main):005:0> a.value
> => "1"
> irb(main):006:0> a + 'foo'
> => "1foo"
> irb(main):007:0> a.value
> => "1"
> irb(main):008:0> a.numeric += 2
> => 3
> irb(main):009:0> a.value
> => "3"
> irb(main):010:0> a.string += 'zzz'
> => "3zzz"
> irb(main):011:0> a.value
> => "3zzz"
> irb(main):012:0>
> -------------------------------------------------------------

Thank you for posting this. I learned several new things about the  
capabilities of TkVariable from it.

Regards, Morton