英文:
Setter method not setting struct property Golang
问题
我需要帮助理解为什么会出现这个错误：
我正在使用指针，因为我希望它更新字段。
> prog.go:56: 无法将MammalImpl字面量（类型为MammalImpl）用作Mammal数组元素的类型：MammalImpl未实现Mammal（SetName方法具有指针接收器）prog.go:57: 无法将MammalImpl字面量（类型为MammalImpl）用作Mammal数组元素的类型：MammalImpl未实现Mammal（SetName方法具有指针接收器）
我不确定为什么无法按照以下方式设置/覆盖名称属性。
package main
import (
"fmt"
)
type Mammal interface {
GetID() int
GetName() string
SetName(s string)
}
type Human interface {
Mammal
GetHairColor() string
}
type MammalImpl struct {
ID int
Name string
}
func (m MammalImpl) GetID() int {
return m.ID
}
func (m MammalImpl) GetName() string {
return m.Name
}
func (m *MammalImpl) SetName(s string) {
m.Name = s
}
type HumanImpl struct {
MammalImpl
HairColor string
}
func (h HumanImpl) GetHairColor() string {
return h.HairColor
}
func Names(ms []Mammal) *[]string {
names := make([]string, len(ms))
for i, m := range ms {
m.SetName("Herbivorous") // 这个修改没有任何效果，并且会抛出错误
names[i] = m.GetName()
}
return &names
}
func main() {
mammals := []Mammal{
MammalImpl{1, "Carnivorious"},
MammalImpl{2, "Ominivorious"},
}
numberOfMammalNames := Names(mammals)
fmt.Println(numberOfMammalNames)
}
Go Playground代码在这里：http://play.golang.org/p/EyJBY3rH23
英文:
I need help with understanding why this error is being thrown:
I am using a pointer because I want it to update the field.
> prog.go:56: cannot use MammalImpl literal (type MammalImpl) as type
> Mammal in array element: MammalImpl does not implement Mammal
> (SetName method has pointer receiver) prog.go:57: cannot use
> MammalImpl literal (type MammalImpl) as type Mammal in array element:
> MammalImpl does not implement Mammal (SetName method has pointer
> receiver)
I am not sure why this is unable to set/override the name property as follows.
package main
import (
"fmt"
)
type Mammal interface {
GetID() int
GetName() string
SetName(s string)
}
type Human interface {
Mammal
GetHairColor() string
}
type MammalImpl struct {
ID int
Name string
}
func (m MammalImpl) GetID() int {
return m.ID
}
func (m MammalImpl) GetName() string {
return m.Name
}
func (m *MammalImpl) SetName(s string) {
m.Name = s
}
type HumanImpl struct {
MammalImpl
HairColor string
}
func (h HumanImpl) GetHairColor() string {
return h.HairColor
}
func Names(ms []Mammal) *[]string {
names := make([]string, len(ms))
for i, m := range ms {
m.SetName("Herbivorous") // This modification is not having any effect and throws and error
names[i] = m.GetName()
}
return &names
}
func main() {
mammals := []Mammal{
MammalImpl{1, "Carnivorious"},
MammalImpl{2, "Ominivorious"},
}
numberOfMammalNames := Names(mammals)
fmt.Println(numberOfMammalNames)
}
Go Playground code is here http://play.golang.org/p/EyJBY3rH23
答案1
得分: 3
问题在于你有一个带有指针接收器的方法SetName()：
func (m *MammalImpl) SetName(s string)
因此，如果你有一个类型为MammalImpl的值，该值的方法集不包含SetName()方法，因此它不实现Mammal接口。
但是，指向MammalImpl的指针（*MammalImpl）的方法集将包含SetName()方法，因此它将实现Mammal接口。
因此，当你填充mammals切片时，你必须使用*MammalImpl值进行填充，因为它实现了切片的元素类型（即Mammal）。如果你已经有一个MammalImpl值，你可以很容易地获得一个指向MammalImpl的指针：使用地址&运算符生成指向该值的指针：
mammals := []Mammal{
&MammalImpl{1, "Carnivorious"},
&MammalImpl{2, "Ominivorious"},
}
在Go Playground上尝试你修改后的程序。
英文:
The problem is that you have a method SetName() which has a pointer receiver:
func (m *MammalImpl) SetName(s string)
So if you have a value of type MammalImpl, the method set of that value does not contain the SetName() method therefore it does not implement the Mammal interface.
But the method set of a pointer to MammalImpl (*MammalImpl) will contain the SetName() method therefore it will implement the Mammal interface.
So when you populate the mammals slice, you have to populate it with *MammalImpl values, because that is the one that implements the element type of the slice (which is Mammal). You can easily obtain a pointer to a MammalImpl if you already have a MammalImpl value: use the address & operator to generate a pointer to the value:
mammals := []Mammal{
&MammalImpl{1, "Carnivorious"},
&MammalImpl{2, "Ominivorious"},
}
Try your modified program on the Go Playground.
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