向下倾斜较高型

Question

是否旁边Box用手工复制内部值一个语言功能向下RatedBox转换为Box？

type Box struct {
    Name string
}

type RatedBox struct {
    Box
    Points int
}

func main() {
    rated := RatedBox{Box: Box{Name: "foo"}, Points: 10}

    box := Box(rated) // does not work
}

去操场

// works, but is quite verbose for structs with more members
box := Box{Name: rated.Name}

Answer 1

在结构中嵌入类型会在结构中添加一个字段,您可以使用非限定类型名称来引用它(不合格意味着省略包名称和可选指针符号).

例如:

box := rated.Box
fmt.Printf("%T %+v", box, box)

输出(在Go Playground上试试):

main.Box {Name:foo}

请注意,赋值会复制该值,因此box局部变量将保存该RatedBox.Box字段值的副本.如果您希望它们是"相同"(指向相同的Box值),请使用指针,例如:

box := &rated.Box
fmt.Printf("%T %+v", box, box)

但这里当然box会有类型*Box.

或者您可以选择嵌入指针类型:

type RatedBox struct {
    *Box
    Points int
}

然后(在Go Playground上试试):

rated := RatedBox{Box: &Box{Name: "foo"}, Points: 10}

box := rated.Box
fmt.Printf("%T %+v", box, box)

最后2的输出:

*main.Box &{Name:foo}