CS 3060: Programming Languages

Ruby

Robert C. Green II, Ph.D.

Day 3

Metaprogramming

Open Classes

You can change the definition of any class at any time

						class NilClass
	def blank?
		true
	end
end

class String
	def blank?
		self.size == 0
	end
end

["", "person", nil].each do |element|
	puts element unless element.blank?
end
						
					

method_missing

						
def self.method_missing(name, *args)
	...
end
						
					

method_missing

						
class Roman
	def self.method_missing name, *args
		roman = name.to_s
		roman.gsub!("IV", "IIII")
		roman.gsub!("IX", "VIIII")
		roman.gsub!("XL", "XXXX")
		roman.gsub!("XC", "LXXXX")
		(roman.count("I") +
		 roman.count("V") * 5 +
		 roman.count("X") * 10 +
		 roman.count("L") * 50 +
		 roman.count("C") * 100)
	end
end

puts Roman.X
puts Roman.XC
puts Roman.XII
puts Roman.X
						
					

Modules

User for "Acts like a..." relationships

as opposed to "Has a..."

						
class ActsAsCsv
	...
	def self.acts_as_csv
		...
	end
	...
end

class RubyCsv < ActsAsCsv
	acts_as_csv
end					
					

Modules

Use for "Acts like a..." relationships

as opposed to "Has a..."

						
class ActsAsCsv
	...
	def self.acts_as_csv
		...
	end
	...
end

class RubyCsv
	include ActsAsCsv
	acts_as_csv
end					
					

Assignment

Read Wrap Up