使用 Ruby 数组的“-”（减法）方法需要什么方法？

Question

如果我有两个数组a 和b，那么包含的对象应该重写什么方法，这样减法- 才能正常工作？

eql?够了吗

编辑

我正在为我的问题添加更多细节。

我已经定义了这个类：

class Instance
    attr_reader :id, :desc 
    def initialize( id ,  desc  )
        @id = id.strip
        @desc = desc.strip
    end

    def sameId?( other )
        @id == other.id
    end

    def eql?( other )
        sameId?( other ) and @desc == other.desc
    end

    def to_s()
        "#{id}:#{desc}"
    end
end

好吗？

然后我从不同的部分填充了我的两个数组，我想得到不同。

a = Instance.new("1","asdasdad")
b = Instance.new("1","a")
c = Instance.new("1","a")

p a.eql?(b) #false
p b.eql?(c) #true 

x = [a,b]
y = [c]

z = x - y # should leave a because b and c "represent" the same object

但这不起作用，因为a 和b 被保存在数组中。我想知道我需要在我的类中重写什么方法才能使其正常工作。

Answer 1

您需要重新定义#eql? 和hash 方法。

你可以这样定义：

def hash
    id.hash + 32 * desc.hash
end

详情：

查看 Ruby 1.9 中调用了什么：

    % irb
    >> class Logger < BasicObject
    >>   def initialize(delegate)
    >>     @delegate = delegate
    >>   end
    >>   def method_missing(m,*args,&blk)
    >>     ::STDOUT.puts [m,args,blk].inspect
    >>     @delegate.send(m,*args,&blk)
    >>   end
    >> end
    => nil
    >> object = Logger.new(Object.new)
    [:inspect, [], nil]
    => #<Object:0x000001009a02f0>
    >> [object] - [0]
    [:hash, [], nil]
    [:inspect, [], nil]
    => [#<Object:0x000001009a02f0>]
    >> zero = Logger.new(0)
    [:inspect, [], nil]
    => 0
    >> [zero] - [0]
    [:hash, [], nil]
    [:eql?, [0], nil]
    => []

在 ruby​​ 1.8.7 中也是如此

    % irb18
    >> class Logger < Object
    >>   instance_methods.each { |m| undef_method m }
    >>   def initialize(delegate)
    >>     @delegate = delegate
    >>   end
    >>   def method_missing(m,*args,&blk)
    >>     ::STDOUT.puts [m,args,blk].inspect
    >>     @delegate.send(m,*args,&blk)
    >>   end
    >> end
    (irb):2: warning: undefining `__send__' may cause serious problem
    (irb):2: warning: undefining `__id__' may cause serious problem
    => nil
    >> object = Logger.new(Object.new)
    [:inspect, [], nil]
    => #<Object:0x100329690>
    >> [object] - [0]
    [:hash, [], nil]
    [:inspect, [], nil]
    => [#<Object:0x100329690>]
    >> zero = Logger.new(0)
    [:inspect, [], nil]
    => 0
    >> [zero] - [0]
    [:hash, [], nil]
    [:eql?, [0], nil]
    => []