Reverse 在 Golang 中是如何工作的？

Question

s := []string{"Zeno", "John", "Al", "Jenny"}

sort.Sort(sort.Reverse(sort.StringSlice(s)))

我无法理解Reverse

的逻辑

Reverse 的源代码如下：

func Reverse(data Interface) Interface {
    return &reverse{data}
}

type reverse struct {
    // This embedded Interface permits Reverse to use the methods of
    // another Interface implementation.
    Interface
}

type Interface interface {
    // Len is the number of elements in the collection.
    Len() int

    // Less reports whether the element with index i
    // must sort before the element with index j.
    //
    // If both Less(i, j) and Less(j, i) are false,
    // then the elements at index i and j are considered equal.
    // Sort may place equal elements in any order in the final result,
    // while Stable preserves the original input order of equal elements.
    //
    // Less must describe a transitive ordering:
    //  - if both Less(i, j) and Less(j, k) are true, then Less(i, k) must be true as well.
    //  - if both Less(i, j) and Less(j, k) are false, then Less(i, k) must be false as well.
    //
    // Note that floating-point comparison (the < operator on float32 or float64 values)
    // is not a transitive ordering when not-a-number (NaN) values are involved.
    // See Float64Slice.Less for a correct implementation for floating-point values.
    Less(i, j int) bool

    // Swap swaps the elements with indexes i and j.
    Swap(i, j int)
}

上面那些给定的操作如何导致给定的数组被反转？

Answer 1

如果你查看 sort.StringSlice 类型，你可以看到它实现了 Less 方法，注意比较 x[i] < x[j]，这意味着较小的元素在前。

func (x StringSlice) Less(i, j int) bool { return x[i] < x[j] }

然后注意 sort.reverse 类型（不是 sort.Reverse 接口），它也实现了 Less 方法，但看看它如何传递 i 和 j 参数，接收 i 和 j 但传递 j 和i，正好等同于 x[i] > x[j]

// Less returns the opposite of the embedded implementation's Less method.
func (r reverse) Less(i, j int) bool {
    return r.Interface.Less(j, i)
}

Reverse 在 Golang 中是如何工作的？

How does Reverse work in Golang under the hood?

reverse

go