Rubyのシングルトンメソッド：オブジェクト単位のカスタマイズ術

str = "Hello"
def str.greet
  "Greetings from #{self}!"
end

puts str.greet # => "Greetings from Hello!"

user1 = "Alice"
user2 = "Bob"

def user1.greet
  "Hello, #{self}!"
end

puts user1.greet # => "Hello, Alice!"
# puts user2.greet # => エラー: undefined method 'greet'

str = "Example"
class << str
  def custom_method
    "This is a singleton method."
  end
end

puts str.custom_method # => "This is a singleton method."

obj = Object.new
singleton_class = class << obj
  self
end

singleton_class.define_method(:unique_method) { "Hello from singleton!" }
puts obj.unique_method # => "Hello from singleton!"

class Example
  def self.class_method
    "I am a class method."
  end
end

puts Example.class_method # => "I am a class method."

module Greetings
  def greet
    "Hello from #{self}!"
  end
end

user = "John"
user.extend(Greetings)
puts user.greet # => "Hello from John!"

obj = Object.new
obj.define_singleton_method(:dynamic_method) { "Dynamic behavior" }
puts obj.dynamic_method # => "Dynamic behavior"

class Example
  def method
    "Instance method"
  end
end

obj = Example.new
def obj.method
  "Singleton method"
end

puts obj.method # => "Singleton method"

class Proxy
  def initialize(target)
    @target = target
  end

  def method_missing(name, *args, &block)
    @target.send(name, *args, &block)
  end
end

target = "Target object"
proxy = Proxy.new(target)

def proxy.special_behavior
  "This is a proxy-specific behavior"
end

puts proxy.special_behavior # => "This is a proxy-specific behavior"