Question

class A
    def p
        puts "1"
    end
end

a = A.new
a.p   #=> "1"

class A
    def p
        puts "2"
    end
end

a.p   #=>"2"

Is this ruby property called “Open Class”?Is there any other language have this property?

Answer 1

Yes, this is called open class in Ruby. Off the top of my head, other languages which have this property include Python and Smalltalk. Also, even though they don’t have classes, mutating a prototype object in ECMAScript, Self, Io and Ioke will have a similar effect.