go - 创建二维 slice 时出错

Question

我正在尝试在 Go 中创建和初始化 2D slice 。虽然以下功能可以正常工作:

func working2D() [][]uint8 {
    p := make([][]uint8, 2)
    for i:=range p{
        p[i]=make([]uint8, 8)
        for j:=range p[i]{
            p[i][j]=uint8(j)
        }
    }
    fmt.Println(p)
    return p
}

Output: [[0 1 2 3 4 5 6 7] [0 1 2 3 4 5 6 7]]

但下面的函数甚至不编译并抛出编译错误:

sample/main/range.go:35:9: v2 declared and not used

func notWorking2D() [][]uint8 {
    p := make([][]uint8, 1)
    for _,v := range p {
        v = make([]uint8, 8)
        for j, v2 := range v {
            v2 = uint8(j)
        }
    }
    fmt.Println(p)
    return p
}

Output: [[],[]]

我在第二个函数中缺少什么？

Answer 1

正如安迪在评论中所说:

The second variable in a range gets set to each value in the slice as the loop iterates. Assigning to that variable does not affect the slice.

你可能只想做:

func notWorking2D() [][]uint8 {
    p := make([][]uint8, 2)
    for i, _ := range p {      
        p[i] = make([]uint8, 8)
        for j, _ := range p[i] {
            p[i][j] = uint8(j)
        }
    }
    return p
}

https://play.golang.org/p/cHQc9ReJBE