# Just found an interesting stuff
x = [[]] * 4 # [[], [], [], []]
x[0] << 1 # or x[0] .push 1
# => [[1], [1], [1], [1]]
x = [[]] * 4 # [[], [], [], []]
# just append an element to the first array of x
update：
x = [[], [], [], []]
x[0] << 1
# => [[1], [], [], []]
据我实验，楼主结论有误。
1] pry(main)> x = [[]] * 4
=> [[], [], [], []]
[2] pry(main)> x
=> [[], [], [], []]
[3] pry(main)> x[0] << 1
=> [1]
[4] pry(main)> x
=> [[1], [1], [1], [1]]
[5] pry(main)> -------------
[5] pry(main)*
[5] pry(main)*
[6] pry(main)> x = [[]] * 4
=> [[], [], [], []]
[7] pry(main)> x
=> [[], [], [], []]
[8] pry(main)> x << 1
=> [[], [], [], [], 1]
[9] pry(main)> x
=> [[], [], [], [], 1]
[10] pry(main)> x[0] << 1
=> [1]
[11] pry(main)> x
=> [[1], [1], [1], [1], 1]
[12] pry(main)>
我估计是这样，这个x = [[]] * 4 是同一个空数组 (的指针) 重复了 4 次，用 x=[[], [], [], []] 才是建立了四个不一样的空数组。
#1 楼 @santochancf よくやった、達也君 :thumbsup:
x = [[]] * 4
puts x.each {|a| puts a.object_id }
x = Array.new(4) { [] }
puts x.each {|a| puts a.object_id }
# >> 70261926896280
# >> 70261926896280
# >> 70261926896280
# >> 70261926896280
# >> 70261926887120
# >> 70261926887100
# >> 70261926887060
# >> 70261926887040
