防止Ruby中的副作用

Question

a = [1,2,3,4]
b = a << 5
a == [1,2,3,4] # returns false

如何分配b到a与5追加到末尾,而无需修改a本身？

Answer 1

只需加两个数组:

a = [1,2,3,4]
b = a + [5]

# b == [1, 2, 3, 4, 5]
# a == [1, 2, 3, 4]

Answer 2

Ruby的变量保持引用对象和=操作复制引用.

看来你希望:clone a

irb(main):001:0> a = [1,2,3,4]
=> [1, 2, 3, 4]
irb(main):002:0> b = a.clone << 5
=> [1, 2, 3, 4, 5]
irb(main):003:0> a
=> [1, 2, 3, 4]
irb(main):004:0> b
=> [1, 2, 3, 4, 5]

Answer 3

我通常这样做：

b = [*a, 5]