Hello, I have this : module Perimeter def perimeter end end class Rectangle include Perimeter def initialize(length, breadth) @length = length @breadth = breadth end def sides [@length, @breadth, @length, @breadth] end end class Square include Perimeter def initialize(side) @side = side end def sides [@side, @side, @side, @side] end end now I can calculate the permiter when using the sides defenition of square and rectangle but how do I know which is the calling class. So I can do something like this : class.sides.each { |sum, x| sum + x } Roelof

on 2014-06-21 11:32

on 2014-06-21 13:17

On Jun 21, 2014, at 5:31 AM, Roelof Wobben <r.wobben@home.nl> wrote: > class Rectangle > > > now I can calculate the permiter when using the sides defenition of square and rectangle > but how do I know which is the calling class. > So I can do something like this : class.sides.each { |sum, x| sum + x } > > Roelof Including the module in a class adds it to the ancestors of the class, so when Ruby searches for methods on a Square or a Rectangle it will search the module after searching the including class. If you consider code like this: s = Square.new(10) puts s.perimeter r = Rectangle.new(4, 5) puts r.perimeter then when you send perimeter to s or r self will be an instance of a particular class, and that determines where to dispatch the sides message to when calculating the perimiter. You can try something like: module Perimeter def perimeter puts "perimiter: operating on a #{self.class}" sides.reduce {|sum, n| sum + n} # That could be shortened to # sides.reduce :+ end end and see what it does. For the sample above I see: ~/tmp ∙ ./try.rb perimiter: operating on a Square 40 perimiter: operating on a Rectangle 18 Hope this helps, Mike -- Mike Stok <mike@stok.ca> http://www.stok.ca/~mike/ The "`Stok' disclaimers" apply.

on 2014-06-21 16:03

Mike Stok schreef op 21-6-2014 13:16: >> end >> end >> end > > module Perimeter > ~/tmp ??? ./try.rb > perimiter: operating on a Square > 40 > perimiter: operating on a Rectangle > 18 > > Hope this helps, > > Mike > Thanks, Roelof