What are #method_missing and #send? Why are they useful?

method_missing, as the name suggests, is called when the method cannot be found. With this powerful meta-programming tool, we can create dynamic methods, such as the dynamic finder in Active Record

class Legislator
# Pretend this is a real implementation
def find(conditions = {})
end

# Define on self, since it's a class method
def self.method_missing(method_sym, *arguments, &block)
# the first argument is a Symbol, so you need to_s it if you want to pattern match
if method_sym.to_s =~ /^find_by_(.*)$/
find($1.to_sym => arguments.first)
else
super
end
end
end

Send is also a powerful tool for dynamic method invocation. Its function is to pass a method to the object in the form of parameters

class Box
def open_1
puts "open box"
end

def open_2
puts "open lock and open box"
end

def open_3
puts "It's a open box"
end

def open_4
puts "I can't open box"
end

def open_5
puts "Oh shit box!"
end
end

box = Box.new

box.send("open_#{num}")