class C
end
var = \"I am a local var outside\"
C.class_eval do
def self.a_class_method
puts var
end
end
I know, this is not correct, beca
Class methods don't really exist in Ruby, they are just singleton methods of the class object. Singleton methods don't really exist, either, they are just ordinary instance methods of the object's singleton class.
Since you already know how to define instance methods (using Module#define_method
), you already know everything you need to know. You just need to call class_eval
on C
's singleton class instead of C
itself:
(class << C; self end).class_eval do
define_method(:a_class_method) do
puts var
end
end
Current versions of Ruby have a singleton_class
method to make that easier:
C.singleton_class.class_eval do
define_method(:a_class_method) do
puts var
end
end
But actually, current versions of Ruby also have Module#define_singleton_method
, so, in this particular case, that is unnecessary:
C.define_singleton_method(:a_class_method) do
puts var
end
you can do it simply this way
class << C
define_method(:a_class_method) do
# do something
end
end
C.instance_eval do
def class_method
"This is class method"
end
end
instance_eval: defines singleton methods on the object (which results in class methods when it's called on class object).
class_eval: defines regular instance methods