For the method invocation expression o.m, Ruby performs name
resolution with the following steps: 1) first, it checks the
eigenclass of o for singleton methods named m. 2) If no method m is
found in the eigenclass, Ruby searches the class of the o for an
instance method named m. 3) If no method m is found in the class, Ruby
searches the instance methods of any modules included by the class of
o. If that class includes more than one module, then they are searched
in the reveerse of the order in which they wre included. That is, the
most recently included module is searched first. If no instance method
m is found in the class of o or in its modules, then the search moves
up the inheirtance hierarchy to the superclass. Steps 2 and 3 are
repeated for each class in the inheritance heirarchy until each
ancestor class and its included modules have been searched. If no
method named m is found after completing the search, then a method
named method_missing is invoked instead. In order to find an
appropriate definition of this method, the name resolution algorithm
starts over at step 1. The kernel module provides a default
implementation of method_missing, so this second pass of name
resolution is guaranteed to succeed.
Notice the part "Steps 2 and 3 are repeated for each class in the
inheritance heirarchy..."
What if the superclass has an eigenclass method? Why doesn't it repeat
Step 1?
The answer is that when Ruby searches for singleton methods in the
eigenclass of an object, it also searches the superclass (and all
ancestors) of the eigenclass as well.
For the method invocation expression o.m, Ruby performs name
resolution with the following steps: 1) first, it checks the
eigenclass of o for singleton methods named m. 2) If no method m is
found in the eigenclass, Ruby searches the class of the o for an
instance method named m. 3) If no method m is found in the class, Ruby
searches the instance methods of any modules included by the class of
o. If that class includes more than one module, then they are searched
in the reveerse of the order in which they wre included. That is, the
most recently included module is searched first. If no instance method
m is found in the class of o or in its modules, then the search moves
up the inheirtance hierarchy to the superclass. Steps 2 and 3 are
repeated for each class in the inheritance heirarchy until each
ancestor class and its included modules have been searched. If no
method named m is found after completing the search, then a method
named method_missing is invoked instead. In order to find an
appropriate definition of this method, the name resolution algorithm
starts over at step 1. The kernel module provides a default
implementation of method_missing, so this second pass of name
resolution is guaranteed to succeed.
Notice the part "Steps 2 and 3 are repeated for each class in the
inheritance heirarchy..."
What if the superclass has an eigenclass method? Why doesn't it repeat
Step 1?
I'm not sure in what scenario 1) would ever be repeated. In any case,
o's superclass's eigenclass is not part of o's inheritance chain:
class Animal
def self.greet
puts 'hi'
end
end
class Dog < Animal
end
o = Dog.new
puts o.class
puts o.class.superclass
o.greet
--output:--
Dog
Animal
1.rb:13:in `<main>': undefined method `greet' for
#<Dog:0x0000010086a050> (NoMethodError)
