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Ruby Programming
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Setting Widget Options

If you look at a Tk reference manual (the one written for Perl/Tk, for example), you'll notice that options for widgets are usually listed with a hyphen---as a command-line option might be. In Perl/Tk, options are passed to a widget in a Hash. You can do that in Ruby as well, but you can also pass options using a code block; the name of the option is used as a method name within the block and arguments to the option appear as arguments to the method call. Widgets take a parent as the first argument, followed by an optional hash of options or the code block of options. Thus, the following two forms are equivalent.

TkLabel.new(parent_widget) {
  text    'Hello, World!'
  pack('padx'  => 5,
       'pady'  => 5,
       'side'  => 'left')
}
# or
TkLabel.new(parent_widget, text => 'Hello, World!').pack(...)

One small caution when using the code block form: the scope of variables is not what you think it is. The block is actually evaluated in the context of the widget's object, not the caller's. This means that the caller's instance variables will not be available in the block, but local variables from the enclosing scope and globals (not that you ever use those) will be. We'll show option passing using both methods in the examples that follow.

Distances (as in the padx and pady options in these examples) are assumed to be in pixels, but may be specified in different units using one of the suffixes ``c'' (centimeter), ``i'' (inch), ``m'' (millimeter), or ``p'' (point).
Ruby Programming
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