双 * (splat) 运算符有什么作用 [英] What does a double * (splat) operator do

问题描述

你见过这样声明的函数吗?

Have you seen a function declared like this?

def foo a, **b
  ...
end

我知道单个 * 是 splat 运算符.** 是什么意思?

I understand that a single * is the splat operator. What does ** mean?

推荐答案

Ruby 2.0 引入了关键字参数，而 ** 的作用类似于 *，但用于关键字参数.它返回一个带有键/值对的哈希.

Ruby 2.0 introduced keyword arguments, and ** acts like *, but for keyword arguments. It returns a Hash with key / value pairs.

对于此代码:

def foo(a, *b, **c)
  [a, b, c]
end

这是一个演示:

> foo 10
=> [10, [], {}]
> foo 10, 20, 30
=> [10, [20, 30], {}]
> foo 10, 20, 30, d: 40, e: 50
=> [10, [20, 30], {:d=>40, :e=>50}]
> foo 10, d: 40, e: 50
=> [10, [], {:d=>40, :e=>50}]

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