Question

在以下代码行中，我期待的结果与实际结果不同。有人能帮助我理解为什么吗？

array1 = [["a", "b", "c"], ["a", "b", "c"]]
temp1 = ["x", "y", "z"]
array1 << temp1

2.times do
  temp1[0] = gets.chomp      #first loop enter 1 and then 4
  temp1[1] = gets.chomp      #first loop enter 2 and then 5
  temp1[2] = gets.chomp      #first loop enter 3 and then 6
  puts temp1.inspect
  array1 << temp1
  puts array1.inspect        
  # Actual result: [["a", "b", "c"], ["a", "b", "c"], ["4", "5", "6"], ["4", "5", "6"], ["4", "5", "6"]]                          
  # Expected Result: [["a", "b", "c"], ["a", "b", "c"], ["x", "y", "z"], ["1", "2", "3"], ["4", "5", "6"]]
end

Answer 1

执行此操作并将其工作（将.clone添加到temp1的所有引用）：

 array1 = [["a", "b", "c"], ["a", "b", "c"]]
 temp1 = ["x", "y", "z"]
 array1 << temp1.clone
 2.times do
      temp1[0] = gets.chomp      #first loop enter 1 and then 4
      temp1[1] = gets.chomp      #first loop enter 2 and then 5
      temp1[2] = gets.chomp      #first loop enter 3 and then 6

      puts temp1.inspect
      array1 << temp1.clone
      puts array1.inspect 

 end

 # Actual result: [["a", "b", "c"], ["a", "b", "c"], ["x", "y", "z"], ["1", "2", "3"], ["4", "5", "6"]]

 # Expected Result: [["a", "b", "c"], ["a", "b", "c"], ["x", "y", "z"], ["1", "2", "3"], ["4", "5", "6"]]

基本上，当您在temp1中附加array1时，它会通过引用而不是按值发生。因此，每当temp1更新时，array1中相应的附加条目也将自动更新。要防止此行为，您需要在将对象附加到数组之前clone / dup。 clone / dup复制对象（因此它没有相同的引用/ object_id），然后分配它。

有关详细说明，请查看this帖子。

Answer 2

每当遇到类似这样的问题时，添加一些代码就可以在计算的每个步骤中打印出每个感兴趣对象的object_id，这是有益的。每个Ruby对象都有一个唯一的object_id。可以使用方法Object.object_id检索id：

{ "a"=>1 }.object_id
  #=> 70225550848400

让我们试一试。（我已将object_id缩短为最后三位数，以便更容易看到它们何时发生变化。）

array1 = [["a", "b", "c"], ["a", "b", "c"]]
puts "1a array1.object_id=#{array1.object_id % 1000}"
puts "1b array1.map(&:object_id)=#{array1.map { |e| e.object_id % 1000 } }"
puts
temp1 = ["x", "y", "z"]
puts "2a temp1.object_id=#{temp1.object_id % 1000}"
array1 << temp1
puts "2b array1=#{array1.inspect}"
puts "2c array1.object_id=#{array1.object_id % 1000}"
puts "2d array1.map(&:object_id)=#{array1.map { |e| e.object_id % 1000 } }"
puts
2.times do
  temp1[0] = gets.chomp
  temp1[1] = gets.chomp
  temp1[2] = gets.chomp
  puts "3a temp1=#{temp1.inspect}"
  puts "3b temp1.object_id=#{temp1.object_id % 1000}"
  array1 << temp1
  puts "3c array1=#{array1.inspect}"
  puts "3d array1.object_id=#{array1.object_id % 1000}"
  puts "3e array1.map(&:object_id)=#{array1.map { |e| e.object_id % 1000 } }"
  puts 
end

打印

1a array1.object_id=900
1b array1.map(&:object_id)=[0, 920]

2a temp1.object_id=480
2b array1=[["a", "b", "c"], ["a", "b", "c"], ["x", "y", "z"]]
2c array1.object_id=900
2d array1.map(&:object_id)=[0, 920, 480]

1
2
3
3a temp1=["1", "2", "3"]
3b temp1.object_id=480
3c array1=[["a", "b", "c"], ["a", "b", "c"], ["1", "2", "3"], ["1", "2", "3"]]
3d array1.object_id=900
3e array1.map(&:object_id)=[0, 920, 480, 480]

4
5
6
3a temp1=["4", "5", "6"]
3b temp1.object_id=480
3c array1=[["a", "b", "c"], ["a", "b", "c"], ["4", "5", "6"], ["4", "5", "6"],
           ["4", "5", "6"]]
3d array1.object_id=900
3e array1.map(&:object_id)=[0, 920, 480, 480, 480]

你需要仔细研究这个。

要了解发生了什么，将数组视为容器可能会有所帮助。你所做的是更改容器的内容，但不更改容器本身，但array1是容器列表。

要使代码正常工作，您只需更改容器和内容即可。一种简单的方法是替换：

temp1[0] = gets.chomp
temp1[1] = gets.chomp
temp1[2] = gets.chomp

与

temp1 = [gets.chomp, gets.chomp, gets.chomp]

array1 = [["a", "b", "c"], ["a", "b", "c"]]
puts "1a array1.object_id=#{array1.object_id % 1000}"
puts "1b array1.map(&:object_id)=#{array1.map { |e| e.object_id % 1000 } }"
puts
temp1 = ["x", "y", "z"]
puts "2a temp1.object_id=#{temp1.object_id % 1000}"
array1 << temp1
puts "2b array1=#{array1.inspect}"
puts "2c array1.object_id=#{array1.object_id % 1000}"
puts "2d array1.map(&:object_id)=#{array1.map { |e| e.object_id % 1000 } }"
puts
2.times do
  temp1 = [gets.chomp, gets.chomp, gets.chomp]
  puts "3a temp1=#{temp1.inspect}"
  puts "3b temp1.object_id=#{temp1.object_id % 1000}"
  array1 << temp1
  puts "3c array1=#{array1.inspect}"
  puts "3d array1.object_id=#{array1.object_id % 1000}"
  puts "3e array1.map(&:object_id)=#{array1.map { |e| e.object_id % 1000 } }"
  puts 
end

打印

1a array1.object_id=100
1b array1.map(&:object_id)=[220, 120]

2a temp1.object_id=660
2b array1=[["a", "b", "c"], ["a", "b", "c"], ["x", "y", "z"]]
2c array1.object_id=100
2d array1.map(&:object_id)=[220, 120, 660]

1
2
3
3a temp1=["1", "2", "3"]
3b temp1.object_id=800
3c array1=[["a", "b", "c"], ["a", "b", "c"], ["x", "y", "z"], ["1", "2", "3"]]
3d array1.object_id=100
3e array1.map(&:object_id)=[220, 120, 660, 800]

4
5
6
3a temp1=["4", "5", "6"]
3b temp1.object_id=580
3c array1=[["a", "b", "c"], ["a", "b", "c"], ["x", "y", "z"], ["1", "2", "3"],
           ["4", "5", "6"]]
3d array1.object_id=100
3e array1.map(&:object_id)=[220, 120, 660, 800, 580]

Ruby附加到数组

2 个答案: