go - 使用闭包在 Go 中编写下一个排列，我的代码有什么问题

Question

我编写了一个使用闭包的函数“iterPermutation”。我想从我做不到的闭包中返回数组和 bool 值。所以只尝试了数组，但它仍然报错

cannot use func literal (type func() []int) as type []int in return argument

我想像这样使用 iterPermutation

a := []int{0,1,2,3,4}
nextPermutation, exists := iterPermutation(a)
for exists {
    nextPermutation()
}

func iterPermutation(a []int) []int {
    return func() []int {
        i := len(a) - 2

        for i >= 0 && a[i+1] <= a[i] {
            i--
        }
        if i < 0 {
            return a
        }

        j := len(a) - 1
        for j >= 0 && a[j] <= a[i] {
            j--
        }

        a[i], a[j] = a[j], a[i]

        for k, l := i, len(a)-1; k < l; k, l = k+1, l-1 {
            a[k], a[l] = a[l], a[k]
        }
        return a
    }
}

Answer 1

Return statements 的 Golang 规范描述:

The return value or values may be explicitly listed in the "return" statement. Each expression must be single-valued and assignable to the corresponding element of the function's result type.

用于置换的函数应包含两个返回值，一个用于数组，另一个用于 bool 值。由于您要从函数返回中分配两个变量:

a := []int{0,1,2,3,4}
nextPermutation, exists := iterPermutation(a) // it should return two values one for nextPermutation which is an array and other is exists which might be a boolean value.
for exists {
    nextPermutation()
}

对于以下错误:

"cannot use func literal (type func() []int) as type []int in return argument"

你返回的 func() 文字包含在置换的闭包函数中以及 bool 值，因此将返回类型更改为:

package main

func main(){
    a := []int{0,1,2,3,4}
    nextPermutation, _ := iterPermutation(a)
        nextPermutation()
}

func iterPermutation(a []int) ((func() []int), bool) { // return both values
    return func() []int {
        i := len(a) - 2

        for i >= 0 && a[i+1] <= a[i] {
            i--
        }
        if i < 0 {
            return a
        }

        j := len(a) - 1
        for j >= 0 && a[j] <= a[i] {
            j--
        }

        a[i], a[j] = a[j], a[i]

        for k, l := i, len(a)-1; k < l; k, l = k+1, l-1 {
            a[k], a[l] = a[l], a[k]
        }
        return a
    }, true // add boolean value to return from the function.
}

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