下标

扩展一个数组的的下标，

传入一个下标的数组，返回这些下标对应的元素的数组

extension Array{

subscript(input : [Int]) ->ArraySlice {

get{

var result =ArraySlice()

for i in input {

assert(i

result.append(self[i])

}

return result

}

set{

for(index, i) in input.enumerated() {

assert(i< self.count,"数组越界")

self[i] = newValue[index]

}

}

}

}

letarray01 = ["a","b","c","d"]

leta01 =array01[0]

letarray02 =array01[[0,1,3]]//类型为ArraySlice ,值为["a", "b", "d"]