Object#tapはこう動いて欲しい!!!!!!

tap_ext.rb

# -*- coding: utf-8 -*-

class Tapped < BasicObject

  private *instance_methods # 全メソッドをmethod_missingへ転送する

  def initialize obj, result=self
    @obj = obj
    @result = result
  end

  def method_missing f, *a, &b
    res = @obj.send f, *a, &b
    if @result.nil? then res else @result end
  end

end

class Object
  def tap result=self
    if block_given?
      res = yield self
      if result.nil? then res else result end
    else
      Tapped.new self, result
    end
  end
end

a = [].tap do |a|
  a << 1
  a << 2
end

p a # => [1, 2]

a = [1, 2, 3].tap nil do |a|
  a.reverse
end

p a # => [3, 2, 1]

obj = Object.new.tap.instance_eval do |obj|
  @attr = "hello"
  def attr
    @attr
  end
end

p obj.attr # => "hello"