[英]Creating a map from an array of struct pointers
我有一个指向结构的指针数组。 结构具有name
字段。 我想创建一个从名称到结构指针的映射。
为什么registry
映射中的所有值都相同?
package main
import "fmt"
type Thing struct {
Name string
Value int
}
type Registry map[string]*Thing
func toRegistry(things *[]Thing) Registry {
registry := make(Registry)
for _, thing := range *things {
registry[thing.Name] = &thing
}
return registry
}
func main() {
things := []Thing{{"thingA", 1}, {"thingB", 2}}
registry := toRegistry(&things)
fmt.Println(registry)
}
样本输出: map[thingB:0x10436180 thingA:0x10436180]
根据@tvblah的建议, things
已经是片切了,所以没有必要指向它:
package main
import "fmt"
type Thing struct {
Name string
Value int
}
type Registry map[string]*Thing
func toRegistry(things []Thing) Registry {
registry := make(Registry)
for _, thing := range things {
registry[thing.Name] = &thing
}
return registry
}
func main() {
things := []Thing{{"thingA", 1}, {"thingB", 2}}
registry := toRegistry(things)
fmt.Println(registry)
每个映射值都是一个指向单个局部变量thing
的指针。
一种解决方法是添加一个指向slice元素的指针:
func toRegistry(things []Thing) Registry {
registry := make(Registry)
for i := range things {
registry[things[i].Name] = &things[i]
}
return registry
}
另一个选择是在切片中存储指向Thing
指针:
func toRegistry(things []*Thing) Registry {
registry := make(Registry)
for _, thing := range things {
registry[thing.Name] = thing
}
return registry
}
func main() {
things := []*Thing{&Thing{"thingA", 1}, &Thing{"thingB", 2}}
registry := toRegistry(things)
fmt.Println(registry)
}
我将函数参数从指向切片的指针更改为切片。 更改不会对问题产生任何影响,但通常是Go代码的编写方式。 切片的指针很少在Go中使用。
您可以在每次迭代中将thing
重新分配给另一个局部变量,并将新变量存储在注册表中。
package main
import "fmt"
type Thing struct {
Name string
Value int
}
type Registry map[string]*Thing
func toRegistry(things *[]Thing) Registry {
registry := make(Registry)
for _, thing := range *things {
t := thing
registry[thing.Name] = &t
}
return registry
}
func main() {
things := []Thing{{"thingA", 1}, {"thingB", 2}}
registry := toRegistry(&things)
fmt.Println(registry)
}
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