Let's open class Module
and add a method to it:
class Module
def foo
puts "phew"
end
end
I can call this method by doing this,
Class.foo
which is understandable because class of Class
is Class
, whose superclass is Module
. so it can call instance methods defined in Module
.
Now, the method bar
below is defined on Module
's eigenclass:
class Module
def self.bar
puts "bar"
end
end
but now
Class.bar
also works.
Can someone explain me how Class
can access methods in Module
's eigenclass?
I think I got it now. Method look up doesn't work the way I explained before. when I do Class.foo
, the method is searched in Class
's eigenclass and then it's superclass which is Module
's eigenclass all the way upto BasicObject
's eigenclass at which point it turns upon itself (like a serpent eating it's own tail) to look for method in Class
(as Class
is the superclass of BasicObject
's eigenclass) and then to it's superclass Module
, where it finds the method.
Similarly, when I do Class.bar
, method is searched in Class
's eigenclass and then in Module
's eigenclass where it finds it.
When I do
class Class
def check
puts "class instance method"
end
end
and
class Module
def self.check
puts "modules eigenclass method"
end
def check
puts "module instance method"
end
end
guess wot is the output when I do:
Class.check
This is my current understanding:
There is a fairly comprehensive overview of Ruby's method lookup behaviour when Eigenclasses are involved in this blog post by Andrea Singh. Notably, the "Eigenclasses and Class Inheritance" section near the very end contains a useful lookup diagram that should address your questions.
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