Question

我在Ruby中有一个由5个空数组组成的数组。我试图使用<<运算符将字符串推入第一个数组，但结果是字符串被推入所有数组。请帮我理解这一点。

预期输出为：

# => [["car"], [], [], [], []]

但我得到了：

# => [["car"], ["car"], ["car"], ["car"], ["car"]]

irb dump：

1.9.3-p194 :001 > output = Array.new(5, [])
 => [[], [], [], [], []] 
1.9.3-p194 :002 > output.inspect
 => "[[], [], [], [], []]" 
1.9.3-p194 :003 > output[0].inspect
 => "[]" 
1.9.3-p194 :004 > output[0] << "car"
 => ["car"] 
1.9.3-p194 :005 > output.inspect
 => "[[\"car\"], [\"car\"], [\"car\"], [\"car\"], [\"car\"]]"

Answer 1

他们都是同一个对象：

ree-1.8.7-2012.02 :001 > output = Array.new(5, [])
 => [[], [], [], [], []] 
ree-1.8.7-2012.02 :002 > output[0]
 => [] 
ree-1.8.7-2012.02 :003 > output[0].object_id
 => 2219989240 
ree-1.8.7-2012.02 :004 > output[1].object_id
 => 2219989240 
ree-1.8.7-2012.02 :005 > output[2].object_id
 => 2219989240 
ree-1.8.7-2012.02 :006 > output[3].object_id
 => 2219989240 
ree-1.8.7-2012.02 :007 > output[4].object_id
 => 2219989240 
ree-1.8.7-2012.02 :008 >

试试这个：

ree-1.8.7-2012.02 :008 > output = []
 => [] 
ree-1.8.7-2012.02 :009 > 5.times{output << []}
 => 5

Answer 2

如Pedro Nascimento指出的那样，如果以这种方式初始化数组，它们都具有相同的对象id。您可以使用similar syntax创建嵌套数组来解决此问题：

irb(main):047:0> output = Array.new(5) {[]}
=> [[], [], [], [], []]
irb(main):048:0> output.each {|i| puts i.object_id}
10941700
10941680
10941660
10941640
10941620

因此，您对output[0]的追加将按预期工作：

irb(main):049:0> output[0] << "cat"
=> ["cat"]
irb(main):050:0> output
=> [["cat"], [], [], [], []]

Answer 3

代码

output = Array.new(5, [])

正在尝试只创建一个对象副本，

所以

ree-1.8.7-2012.02 :003 > output[0].object_id
 => 2219989240 
ree-1.8.7-2012.02 :004 > output[1].object_id
 => 2219989240 
ree-1.8.7-2012.02 :005 > output[2].object_id
 => 2219989240 
ree-1.8.7-2012.02 :006 > output[3].object_id
 => 2219989240 
ree-1.8.7-2012.02 :007 > output[4].object_id
 => 2219989240

如果要创建多个对象副本，请使用此

     output = Array.new(5) {[]}    #=> [[], [], [], [], []]

代码

 output.each {|i| puts i.object_id}

会告诉你

1.9.3-p194 :005 >  output.each {|i| puts i.object_id}
13417360
13417340
13417320
13417300
13417280
 => [[], [], [], [], []]

将字符串压入数组中的数组会产生意外结果

3 个答案: