Ruby switches
in [Ruby]
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From: Kenneth on 7 Jul 2010 08:09 Let's say I have something like this case when "".empty? then puts "Empty" when "".nil? then puts "Nil" when "".include?("a") then puts "Includes 'a'" end Is there a way to do something like this instead? (This does not work since the methods in the switches are acting on Object instead of "".) case "" when empty? then puts "Empty" when nil? then puts "Nil" when include?("a") then puts "Includes 'a'" end -- Posted via http://www.ruby-forum.com/.
From: Brian Candler on 7 Jul 2010 08:40 Kenneth wrote: > Let's say I have something like this > > case > when "".empty? then puts "Empty" > when "".nil? then puts "Nil" > when "".include?("a") then puts "Includes 'a'" > end > > Is there a way to do something like this instead? (This does not work > since the methods in the switches are acting on Object instead of "".) > > case "" > when empty? then puts "Empty" > when nil? then puts "Nil" > when include?("a") then puts "Includes 'a'" > end case str when "": puts "Empty" when nil: puts "Nil" when /a/: puts "Includes 'a'" end The case statement actually expands to the === operator, so this is equivalent to if "" === str puts "Empty" elsif nil === str puts "Nil" elsif /a/ === str puts "Includes 'a'" end The === operator does the "right thing" in each of these cases. -- Posted via http://www.ruby-forum.com/.
From: Kenneth on 7 Jul 2010 08:53 Hi, the point I was trying to make was sending a boolean method to the case. Let's say I have a User object and it has instance methods banned? and activated? They are either true or false. Instead of doing case when user.banned? then ... when user.activated? then ... end I was hoping there would be something like case user when banned? then ... when activated? then ... end I would like to see something like this but it seems hard to implement. -- Posted via http://www.ruby-forum.com/.
From: Kenneth on 7 Jul 2010 09:03 I guess you can define a new method inside the class like this when possible, as long as your then statements are nice. class User def status case when banned? then ... when activated? then ... end end end -- Posted via http://www.ruby-forum.com/.
From: Brian Candler on 7 Jul 2010 09:04
Kenneth wrote: > Hi, the point I was trying to make was sending a boolean method to the > case. Then no, there is not a variant of the case statement which does this. > I was hoping there would be something like > case user > when banned? then ... > when activated? then ... > end If you want to invoke method 'banned?' on a particular object, then you have to send it to that object. A bare called to 'banned?' is invoked on the current object (self). But here are a couple of alternatives to consider: user = Object.new def user.banned?; false; end def user.activated?; true; end # Example 1 user.instance_eval { case when banned?; puts "Banned!" when activated?; puts "Activated!" end } # Example 2 [ [:banned?, lambda { puts "Banned!" }], [:activated?, lambda { puts "Activated!" }], ].each do |method, action| user.send(method) && (action[]; break) end However if it's only a handful of conditions I'd be inclined to write when user.banned? when user.activated? -- Posted via http://www.ruby-forum.com/. |