golang - 如何在结构中初始化地图字段? [英] golang - how to initialize a map field within a struct?
问题描述
我对初始化包含地图的结构的最佳方法感到困惑.运行此代码会产生 panic: runtime error: assignment to entry in nil map
:
I'm confused about the best way to initialize a struct that contains a map. Running this code produces panic: runtime error: assignment to entry in nil map
:
package main
type Vertex struct {
label string
}
type Graph struct {
connections map[Vertex][]Vertex
}
func main() {
v1 := Vertex{"v1"}
v2 := Vertex{"v2"}
g := new(Graph)
g.connections[v1] = append(g.coonections[v1], v2)
g.connections[v2] = append(g.connections[v2], v1)
}
一个想法是创建一个构造函数,如这个答案.
One idea is to create a constructor, as in this answer.
另一个想法是使用一个 add_connection
方法,如果地图为空,它可以初始化地图:
Another idea is to use an add_connection
method that can initialize the map if it's empty:
func (g *Graph) add_connection(v1, v2 Vertex) {
if g.connections == nil {
g.connections = make(map[Vertex][]Vertex)
}
g.connections[v1] = append(g.connections[v1], v2)
g.connections[v2] = append(g.connections[v2], v1)
}
还有其他选择吗?只是想看看是否有一种普遍接受的方法来做到这一点.
Are there other options? Just wanted to see if there is a commonly-accepted way to do this.
推荐答案
我可能会使用构造函数来做到这一点:
I would probably use a constructor to do this:
func NewGraph() *Graph {
var g Graph
g.connections = make(map[Vertex][]Vertex)
return &g
}
我在标准中找到了这个例子image/jpeg
包(虽然没有地图,但有切片):
I've found this example in the standard image/jpeg
package (not with a map though, but with a slice):
type Alpha struct {
Pix []uint8
Stride int
Rect Rectangle
}
func NewAlpha(r Rectangle) *Alpha {
w, h := r.Dx(), r.Dy()
pix := make([]uint8, 1*w*h)
return &Alpha{pix, 1 * w, r}
}
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