新旧两种方式定义singleton method
class A class << self def class_name to_s end endendA.define_singleton_method(:who_am_i) do "I am: #{class_name}"endA.who_am_i # ==> "I am: A"guy = "Bob"guy.define_singleton_method(:hello) { "#{self}: Hello there!" }guy.hello #=> "Bob: Hello there!"class Fred def initialize(p1, p2) @a, @b = p1, p2 endendfred = Fred.new('cat', 99)fred.instance_variable_get(:@a) #=> "cat"fred.instance_variable_get("@b") #=> 99class Fred def initialize(p1, p2) @a, @b = p1, p2 endendfred = Fred.new('cat', 99)fred.instance_variable_set(:@a, 'dog') #=> "dog"fred.instance_variable_set(:@c, 'cat') #=> "cat"fred.inspect #=> "#<Fred:0x401b3da8 @a="dog", @b=99, @c="cat">"class Dummy attr_reader :var def initialize @var = 99 end def remove remove_instance_variable(:@var) endendd = Dummy.newd.var #=> 99d.remove #=> 99d.var #=> nilclass B def self.run(method) singleton_class = class << self; self; end singleton_class.send(:define_method, method) do puts "Method #{method}" end endend[:failure, :error, :success].each do |method| define_method method do self.state = method endend#Dynamically defining methods in a loop creates a more concise definition, but it's not a particularly readable one. To address this issue I define the def_each method. The motivation for defining a def_each method is that it is easy to notice and understand while scanning a source file.class Class def def_each(*method_names, &block) method_names.each do |method_name| define_method method_name do instance_exec method_name, &block end end endend