Can class methods be added to some instances of Ruby objects but not others?

Question

Here is a module containing some methods:

module M
  def x; y; end
  def y; ...; end
end

Here's a class:

class C
  def z; ...; end
end

I have two instances of C:

 c1 = C.new
 c2 = C.new

Is there something I can do to c1 such that c1.class has x and y, but c2.class doesn't? I don't see a straightforward way to subvert the method lookup.

Answer 1

You could override c1.class to return something other than C (and that other thing would extend M). Other than that, no.

Note that overriding c1.class is almost certainly a bad idea. An object shouldn't lie about what its class is.

Answer 2

Rather than doing c1.class.x, why not do c1.x, as the Law Of Demeter would suggest?

class C
  def self.x
    "hi"
  end
end

c1 = C.new
c2 = C.new
def c1.x
  self.class.x
end
c1.x # => "hi"
c2.x # NoMethodError

Answer 3

Maybe this

c1.extend(M)

c1.methods & [:x, :y] #=> [:x, :y]
c2.methods & [:x, :y] #=> []