需要什麼方法讓「 - 」（減法）方法與Ruby數組一起工作？

Question

如果我有兩個數組a和b，包含的對象必須覆蓋哪種方法，這樣減法-才能正常工作？

與eql?

編輯

我添加更多的細節，我的問題是否足夠。

我有這個類中定義：

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 

好嗎？

然後我從不同部分填充了我的兩個數組，然後我想獲得差異。

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 

但是這是行不通的，因爲a和b被關押在數組中。我想知道我需要在我的課程中重寫什麼方法才能正常工作。

Answer 1

您需要重新定義#eql?和hash方法。

你可以將其定義爲：

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

詳情：

要看看什麼東西被稱爲紅寶石1.9：

% 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] 
    => [] 

同樣是在紅寶石真正1.8.7

% 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] 
    => []