ruby splat运算符在多次赋值期间如何获得数组的第一个和其余部分？

Question

在ruby中，可以将多个赋值与splat运算符组合，以模拟函数语言中的第一个和休息（或头部和尾部）。

first, *rest = [1,2,3,4]  
first # output: 1
rest # output: [2,3,4]

splat运营商如何实现这一目标？

Answer 1

您可以在多个赋值中最多拥有一个splat运算符，并且splat运算符将调整数组的长度以完全匹配右侧的数组。换句话说：

1）当左侧的变量数量大于右侧数组的长度时，带有splat的变量将被赋予一个空数组：

*a = []
# => a == []

*a, b = [1]
# => a == [], b == 1

a, *b = [1]
# => a == 1, b == []

*a, b, c = [1, 2]
# => a == [], b == 1, c == 2

a, *b, c = [1, 2]
# => a == 1, b == [], c == 2

a, b, *c = [1, 2]
# => a == 1, b == 2, c == []

...

2）否则，带有splat的变量将扩展为从右侧填充其余元素：

*a = [1, 2]
# => a == [1, 2]

*a, b = [1, 2, 3]
# => a == [1, 2], b == 3

a, *b = [1, 2, 3]
# => a == 1, b == [2, 3]

*a, b, c = [1, 2, 3, 4]
# => a == [1, 2], b == 3, c == 4

a, *b, c = [1, 2, 3, 4]
# => a == 1, b == [2, 3], c == 4

a, b, *c = [1, 2, 3, 4]
# => a == 1, b == 2, c == [3, 4]

....