英文:
Returning interfaces in Golang
问题
我正在尝试在一个结构体上编写一个方法，该方法接受一个接口类型，并将该接口类型转换为相应的类型后返回。
type Model interface {
GetEntity()
}
type TrueFalseQuestions struct {
//一些内容
}
func (q *TrueFalseQuestions) GetEntity() {
//一些内容
}
type MultiQuestions struct {
//一些内容
}
func (q *MultiQuestions) GetEntity() {
//一些内容
}
type Manager struct {
}
func (man *Manager) GetModel(mod Model) Model {
mod.GetEntity()
return mod
}
func main() {
var man Manager
q := TrueFalseQuestions{}
q = man.GetModel(&TrueFalseQuestions{})
}
所以当我使用TrueFalseQuestions类型调用GetModel()时，我希望自动返回一个TrueFalseQuestions类型。我认为这意味着我的GetModel()方法应该返回一个Model类型。这样，如果我传递一个MultiQuestion类型，就会返回一个MultiQuestion结构体。
英文:
I am trying to write a method on a struct that takes in a interface type and returns that interface type but converted to the appropriate type.
type Model interface {
GetEntity()
}
type TrueFalseQuestions struct {
//some stuff
}
func (q *TrueFalseQuestions) GetEntity() {
//some stuff
}
type MultiQuestions struct {
//some stuff
}
func (q *MultiQuestions) GetEntity() {
//some stuff
}
type Manager struct {
}
func (man *Manager) GetModel(mod Model) Model {
mod.GetEntity()
return mod
}
func main() {
var man Manager
q := TrueFalseQuestions {}
q = man.GetModel(&TrueFalseQuestions {})
}
So when I call GetModel() with type TrueFalseQuestions I want to automatically return a TrueFalseQuestions type. I figured that would mean that my GetModel() method should return a Model type. That way if I pass a MultiQuestion type a MultiQuestion struct is returned.
答案1
得分: 4
当返回类型为Model时，你不能直接返回TrueFalseQuestions。它将始终被隐式地包装在Model接口中。
要获取TrueFalseQuestions，你需要使用类型断言（还需要注意指针和值之间的区别）。
// 这应该是一个指针，因为接口方法都有指针接收器
q := &TrueFalseQuestions{}
q = man.GetModel(&TrueFalseQuestions{}).(*TrueFalseQuestions)
当然，如果你得到了MultiQuestions，这可能会引发恐慌，所以你应该检查ok值，或者使用类型切换。
switch q := man.GetModel(&TrueFalseQuestions{}).(type) {
case *TrueFalseQuestions:
// q 是 TrueFalseQuestions
case *MultiQuestions:
// q 是 MultiQuestions
default:
// 意外的类型
}
英文:
You can't directly return a TrueFalseQuestions when the return type is Model. It will always be implicitly wrapped in a Model interface.
To get the TrueFalseQuestions back, you need to use a type-assertion. (you also need watch out for pointers vs values)
// this should be a pointer, because the interface methods all have pointer receivers
q := &TrueFalseQuestions{}
q = man.GetModel(&TrueFalseQuestions{}).(*TrueFalseQuestions)
That of course can panic if you got a MultiQuestions, so you should check the ok value, or use a type switch
switch q := man.GetModel(&TrueFalseQuestions{}).(type) {
case *TrueFalseQuestions:
// q isTrueFalseQuestions
case *MultiQuestions:
// q is MultiQuestions
default:
// unexpected type
}
答案2
得分: 1
你可以使用类型断言来对返回的值进行断言。
func main() {
var man Manager
tfq := &TrueFalseQuestions{}
q := man.GetModel(tfq)
if v, ok := q.(*TrueFalseQuestions); ok {
fmt.Println("v is true/false", v)
} else if v, ok := q.(*MultiQuestions); ok {
fmt.Println("v is mq", v)
} else {
fmt.Println("unknown", q)
}
}
英文:
You can't, however you can use type assertion on the returned value.
func main() {
var man Manager
tfq := &TrueFalseQuestions{}
q := man.GetModel(tfq)
if v, ok := q.(*TrueFalseQuestions); ok {
fmt.Println("v is true/false", v)
} else if v, ok := q.(*MultiQuestions); ok {
fmt.Println("v is mq", v)
} else {
fmt.Println("unknown", q)
}
}
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