ruby - 将哈希附加到数组

Question

这个练习我有点问题，你能帮我吗？我尝试编辑脚本，但每次创建新实例时，最后一个元素都会覆盖其他元素(即 )

该类必须为后续 block 的组合提供功能:即它必须能够从前一个 block 继承尚未为当前 block 显式定义的指令。

blocks = [] 

blocks << Block.new({ X:0, Y:100, Z:20}) # p blocks:({ X:0, Y:100, Z:20}) 

blocks << Block.new({X:100}, blocks[-1]) #p blocks:({ X:100, Y:100, Z:20},{ X:100, Y:100, Z:20})

blocks << Block.new({Y:0}, blocks[-1]) #p blocks:({ X:100, Y:0, Z:20},{ X:100, Y:0, Z:20},{ X:100, Y:0, Z:20})

我的问题代码是:

#!/usr/bin/env ruby

    class Block


      $instance_2 = true
      $instance_3 = true


      attr_reader :out


      def initialize(out, previous = nil )

        @out = update(out, previous)
      end # end initialize


      def update(actual, previous)
        puts "IN UPDATE: box is: #{previous}"
        box = previous
        if box != nil      
          puts "IF: changing is: #{actual}"
          actual.each do |key, value|
            box[key] = value               
          end  
           box  
        else
          puts "ELSE"
             actual   
        end # end if 
      end # end update

      def inspect
        @out
      end



    end # end Block

    blocks = []
    puts "\n#----------------------1 INSTANCE----------------------#" 
    blocks << Block.new({G: "00", X: 100, Y:100, Z: 100})
    puts "\n#----------------------blocks element----------------------#" 
    p blocks
    puts "last block is: #{blocks[-1].out}"

    puts "\n#----------------------2 INSTANCE----------------------#"  if $instance_2
    blocks << Block.new({G: "01"}, blocks[-1].out) if $instance_2 
    puts "\n#----------------------blocks element----------------------#"if $instance_2 
    p blocks if $instance_2
    puts "last block is: #{blocks[-1].out}"


    puts "\n#----------------------3 INSTANCE----------------------#" if $instance_3
    blocks << Block.new({G: "02"}, blocks[-1].out) if $instance_3 
    puts "\n#----------------------blocks element----------------------#" if $instance_3
    p blocks if $instance_3
    puts "last block is: #{blocks[-1].out}"

    puts "\n#----------------------4 INSTANCE----------------------#" if $instance_3
    blocks << Block.new({G: "03"}, blocks[-1].out) if $instance_3 
    puts "\n#----------------------blocks element----------------------#" if $instance_3
    p blocks if $instance_3
    puts "last block is: #{blocks[-1].out}"

Answer 1

这个问题不是很清楚，但是如果我理解正确的话，可以提供一个可以接受也可以不接受前一个 block 的类。你觉得这样的事情怎么样？

#!/usr/bin/env ruby

class Block < Hash

  def initialize(h, b=nil)
    [:x, :y, :z].each do |s|
      # We start by trying to assign the coordinate that is in the 
      # input hash
      if h[s]
        self[s] = h[s]
      else
      # If the coordinate is not in h, we check for it in b, but we have to
      # remember that if the block that we are providing in b does not have
      # the method :[] or the coordinate is nil we may raise an exception
        begin
          self[s] = b[s]
          raise if not self[s]
        rescue
          raise(Exception, "Cannot initialize block.")   
        end  
      end
    end 
  end

  def inspect
    "block:(x: #{self[:x]}, y: #{self[:y]}, z: #{self[:z]}"
  end
end

# Let's try it!
blocks = [] 
blocks << Block.new({ x:0, y:100, z:20}) 
puts blocks
puts
blocks << Block.new({x:100}, blocks[-1]) 
puts blocks
puts
blocks << Block.new({y:0}, blocks[-1])
puts blocks
puts

关于您的代码

我们只考虑更新方法:

def update(actual, previous)
    puts "IN UPDATE: box is: #{previous}"
    box = previous                 # ! ! ! ! ! ! ! ! WHOOPS!
    if box != nil      
      puts "IF: changing is: #{actual}"
      actual.each do |key, value|
        box[key] = value               
      end  
       box  
    else
      puts "ELSE"
         actual   
    end # end if 
  end # end update

“哎呀”行是造成您问题的原因。用那条线您正在将对 previous 的引用(您的对象变量实际上包含一个引用)提供给 box 变量。当您对 box 执行某些操作时，您实际上正在做的是修改两个变量指向的内容。

您可以立即测试我所说的内容。尝试以这种方式修改该行:

box = previous.clone if previous

(nil 没有 #clone 方法，if 背后的原理)。如果你再次运行它，你会得到一个没有被修改的 block 列表。这不是一段高效的代码，您真的应该重新考虑 update 方法代码。