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start web wide world If the interface to Button changes, this could involve us in a lot of maintenance. Second, the actions performed when a button is pressed are expressed at the wrong level; they are not a feature of the button, but are a feature of the jukebox that uses the buttons. We can fix both of these problems using blocks. class JukeboxButton < Button def initialize(label, &action) super(label) @action = action end def buttonPressed @action.call(self) end end bStart = JukeboxButton.
start web wide world new("Start") { songList.start } bPause = JukeboxButton.new("Pause") { songList.pause } The key to all this is the second parameter to JukeboxButton#initialize. If the last parameter in a method definition is prefixed with an ampersand (such as &action), Ruby looks for a code block whenever that method is called.
start web wide world That code block is converted to an object of class Proc and assigned to the parameter. You can then treat the parameter as any other variable. In our example, we assigned it to the instance variable @action. When the callback method buttonPressed is invoked, we use the Proc#call method on that object to invoke the block. So what exactly do we have when we create a Proc object? The interesting thing is that it's more than just a chunk of code.
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