Map不更新:Map值是固定大小的数组

Question

我在一个结构中有一个映射:

type Neighborhood struct {
rebuilt map[uint32][3]uint32 // Facet index vs {neighbor0, neighbor1, neighbor2}
}

初始化map:

n := &Neighborhood{
rebuilt: make(map[uint32][3]uint32, 9348),
}
// Populate neighbors with default of UINT32_MAX
for i := uint32(0); i < 9348; i++ {
n.rebuilt[i] = [3]uint32{math.MaxUint32, math.MaxUint32, math.MaxUint32}
}

稍后需要更新地图，但这不起作用:

nbrs0 := n.rebuilt[4]
nbrs1 := n.rebuilt[0]
nbrs0[2] = 0
nbrs1[1] = 4

映射是而不是实际上是用上面的赋值语句更新的。我错过了什么?

Answer 1

您需要重新为map分配数组。

nbrs0 := n.rebuilt[4]
nbrs1 := n.rebuilt[0]
nbrs0[2] = 0
nbrs1[1] = 4
n.rebuilt[4] = nrbs0
n.rebuilt[0] = nrbs1

当你赋值给nbrsN时，你复制了原始数组。因此，更改不会传播到map，您需要显式地使用新数组更新map。

Answer 2

你需要赋值回映射条目…

package main
import (
"fmt"
"math"
)
type Neighborhood struct {
rebuilt map[uint32][3]uint32 // Facet index vs {neighbor0, neighbor1, neighbor2}
}
func main() {
n := &Neighborhood{
rebuilt: make(map[uint32][3]uint32, 9348),
}
// Populate neighbors with default of UINT32_MAX
for i := uint32(0); i < 3; i++ {
n.rebuilt[i] = [3]uint32{math.MaxUint32, math.MaxUint32, math.MaxUint32}
}
v := n.rebuilt[1]
v[1] = uint32(0)
fmt.Printf("%vn", v)
fmt.Printf("%vn", n)
n.rebuilt[1] = v
fmt.Printf("%vn", n)
}

https://play.golang.org/p/Hk5PRZlHUYc