Advanced Rails - Building Industrial-Strength Web Apps in Record Time

Ruby Foundations | 11

module B

include A

def hello

"Hello from B"

end

end

module C

include A

def hello

"Hello from C"

end

end

class D

include B

include C

end

D.new.hello # => "Hello from C"

And if we change the order of inclusion, the result changes correspondingly:

class D

include C

include B

end

D.new.hello # => "Hello from B"

In this last example, whereBis included last, the object graph looks like Figure 1-7
(for simplicity, pointers toObject andClass have been elided).

Figure 1-6. The diamond problem of multiple inheritance

A

BC

D