Question

我试图了解Ruby类以及attr_accessor附带的自动生成的getter和setter。为什么下面的代码，我能够得到它但没有设置它？此外，稍后在代码（未显示）中设置适用于我的store实例变量。从read here开始，似乎attr_accessor我应该阅读和写作。

class HashMap
    attr_accessor :store, :num_filled_buckets, :total_entries

    def initialize(num_buckets=256)
        @store = []
        @num_filled_buckets = 0
        @total_entries = 0
        (0...num_buckets).each do |i|
            @store.push([])
        end
        @store
    end

    def set(key, value)
        bucket = get_bucket(key)
        i, k, v = get_slot(key)

        if i >= 0
            bucket[i] = [key, value]
        else
            p num_filled_buckets # <- this works
            num_filled_buckets = num_filled_buckets + 1 if i == -1 # this does not
            # spits out NoMethodError: undefined method `+' for nil:NilClass
            total_entries += 1
            bucket.push([key, value])
        end
    end
...

Answer 1

attr_accessor：num_filled_buckets给你的是两个方法，一个读者和一个作家

def num_filled_buckets
  @num_filled_buckets
end

def num_filled_buckets=(foo)
  @num_filled_buckets = foo
end

返回实例变量@num_filled_buckets的reader方法。一个write方法，它接受一个将写入@num_filled_buckets

的参数

我的下面是你的课程的简化版。

class HashMap
  attr_accessor :num_filled_buckets

  def initialize(num_of_buckets=256)
   @num_filled_buckets = 0
  end

  def set
    p num_filled_buckets #calls the reader method num_filled_buckets 
    p @num_filled_buckets #instance variable @num_filled_buckets
    @num_filled_buckets = @num_filled_buckets + 1
    p @num_filled_buckets
  end
end

hm = HashMap.new
hm.set 
# will output
# 0
# 0
# 1

attr_accessor不适用于Ruby类中的变量设置

1 个答案: