ruby x[0...i] 做什么

Question

我不明白这段代码:

a = [ "a!", "b!", "c!", "d!" ]
a.collect!.with_index {|x, i| x[0...i]}
a #=> ["", "b", "c!", "d!"]

在 collect 行中，x[0...i] 做了什么？我看到了输出，但不明白它是如何做/得到它的。

Answer 1

根据docs :

Ranges constructed using .. run from the beginning to the end inclusively. Those created using ... exclude the end value..

所以 a..b就像a <= x <= b ，而 a...b就像a <= x < b .即:

>> "a!"[0...0]
=> ""
>> "a!"[0...1]
=> "a"
>> "a!"[0...2]
=> "a!"

---

在你的a.collect!.with_index , x 的值和 i将是:

• “一个!” - 0 => "a!"[0...0] => ""
• “啊!” - 1 => "b!"[0...1] => "b"
• “c!” - 2 => "c!"[0...2] => "c!"
• 等等...