How to dynamically define a class method which will refer to a local variable outside?
Solution 1
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
Solution 2
you can do it simply this way
class << C
define_method(:a_class_method) do
# do something
end
end
Croplio
Updated on July 18, 2022Comments
-
Croplio almost 2 years
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, because the
def
created a new scope. I also know that usedefine_method
can create a instance method without creating a new scope, but my point is how to define a class method.