英文:
Golang generic not working when used as map element
问题
我创建了一个MapKeys泛型和List泛型，但是当我将List泛型与普通的map[string]List[int]一起使用时，无法调用泛型的方法，我错在哪里？非常感谢任何想法！
泛型代码如下：
package mainimport "fmt"func MapKeys[K comparable, V any](m map[K]V) []K {r := make([]K, 0, len(m))for k := range m {r = append(r, k)}return r}type List[T any] struct {head, tail *element[T]}type element[T any] struct {next *element[T]val T}func (lst *List[T]) Push(v T) {if lst.tail == nil {lst.head = &element[T]{val: v}lst.tail = lst.head} else {lst.tail.next = &element[T]{val: v}lst.tail = lst.tail.next}}func (lst *List[T]) GetAll() []T {var elems []Tfor e := lst.head; e != nil; e = e.next {elems = append(elems, e.val)}return elems}func main() {var m = map[int]string{1: "2", 2: "4", 4: "8"}fmt.Println("keys m:", MapKeys(m))_ = MapKeys[int, string](m)var yx = make(map[string]List[int])yx["one"] = List[int]{}yx["one"].Push(10)lst := List[int]{}lst.Push(10)lst.Push(13)lst.Push(23)fmt.Println("list:", lst.GetAll())}
调用这行代码：
yx["one"].Push(10)
得到错误消息：
./prog.go:49:12: 无法在List[int]上调用指针方法Push
你可以在这里运行这段代码。
英文:
I created a MapKeys generic and List generic, but when using List generic with normal map[string]List[int], I can't call the generic's method, what I am wrong? any ideas will be very appreciated!
generic code like this :
package mainimport "fmt"func MapKeys[K comparable, V any](m map[K]V) []K {r := make([]K, 0, len(m))for k := range m {r = append(r, k)}return r}type List[T any] struct {head, tail *element[T]}type element[T any] struct {next *element[T]val T}func (lst *List[T]) Push(v T) {if lst.tail == nil {lst.head = &element[T]{val: v}lst.tail = lst.head} else {lst.tail.next = &element[T]{val: v}lst.tail = lst.tail.next}}func (lst *List[T]) GetAll() []T {var elems []Tfor e := lst.head; e != nil; e = e.next {elems = append(elems, e.val)}return elems}func main() {var m = map[int]string{1: "2", 2: "4", 4: "8"}fmt.Println("keys m:", MapKeys(m))_ = MapKeys[int, string](m)var yx = make(map[string]List[int])yx["one"] = List[int]{}yx["one"].Push(10)lst := List[int]{}lst.Push(10)lst.Push(13)lst.Push(23)fmt.Println("list:", lst.GetAll())}
call this line :
yx["one"].Push(10)
got the error message :
./prog.go:49:12: cannot call pointer method Push on List[int]
you can play the code here
答案1
得分: 2
List.Push()具有指针接收器，但您在映射中存储的是非指针，并且无法对映射进行索引取地址操作。详细信息请参见https://stackoverflow.com/questions/57321933/cannot-take-the-address-of-map-element/57322003#57322003。
在映射中存储指针，然后您可以在映射索引结果上调用具有指针接收器的方法：
var yx = make(map[string]*List[int])yx["one"] = &List[int]{}yx["one"].Push(10)
在Go Playground上尝试一下。
注意：如果值是可寻址的，例如变量，您可以在非指针值上调用具有指针接收器的方法：
lst := List[int]{}lst.Push(10)
上述的lst.Push(10)是(&lst).Push(10)的简写形式。详细信息请参见https://stackoverflow.com/questions/46956290/pointer-methods-on-non-pointer-types/46956348#46956348。
英文:
List.Push() has pointer receiver, but you store non-pointers in the map, and indexing maps is not addressable. For details see https://stackoverflow.com/questions/57321933/cannot-take-the-address-of-map-element/57322003#57322003.
Store pointers in the map, and then you can call methods with pointer receivers on map index results:
var yx = make(map[string]*List[int])yx["one"] = &List[int]{}yx["one"].Push(10)
Try it on the Go Playground.
Note: you can call methods with pointer receiver on non-pointer values if the value is addressable, such as a variable:
lst := List[int]{}lst.Push(10)
The above lst.Push(10) is a shorthand for (&lst).Push(10). For details see https://stackoverflow.com/questions/46956290/pointer-methods-on-non-pointer-types/46956348#46956348.
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