Eloquent Ruby 读书笔记 续_Ruby_编程开发_程序员俱乐部

运算符重载和Ruby风格的运算符重载
程序大概意思是，重新定义，文件类的比较方法。只要目录和文件名一样，就说这两个文件类一样。ruby的

class DocumentPointer
  attr_reader :folder, :name
  def initialize( folder, name )
    @folder = folder
    @name = name
  end
  def ==(other)
    return true if other.equal?(self)
    return false unless other.instance_of?(self.class)
    folder == other.folder && name == other.name
  end
end

class DocumentPointer
  attr_reader :folder, :name
  def initialize( folder, name )
    @folder = folder
    @name = name
  end
  def ==(other)
    return false unless other.respond_to?(:folder)
    return false unless other.respond_to?(:name)
    folder == other.folder && name == other.name
  end
end

当我们用的时候

#Asymmetry
class ContractIdentifier < DocumentIdentifier
end

doc_id = DocumentIdentifier.new( 'contracts', 'Book Deal' )
con_id = ContractIdentifier.new( 'contracts', 'Book Deal' )

puts "They are equal!" if doc_id == con_id

会出现子类没有父类方法的问题，在contractIdentifier里没有重载caozuofu.html" target="_blank">操作符。那么

class VersionedIdentifier < DocumentIdentifier
  attr_reader :version

  def initialize(folder, name, version)
    super(folder, name)
    Well-Behaved Equality 147
    @version = version
  end

  def ==(other)
    if other.instance_of? VersionedIdentifier
      other.folder == folder &&
      other.name == name &&
      other.version == version
    elsif other.instance_of? DocumentIdentifier
      other.folder == folder && other.name == name
    else
      false
    end
  end
end