data-structures - 了解嵌套结构

Question

我试图理解 go 中的嵌套结构，所以我做了一个小测试:( playground )

type A struct {
    a string
}

type B struct {
    A
    b string
}

func main() {
    b := B{A{"a val"}, "b val"}

    fmt.Printf("%T -> %v\n", b, b)   // B has a nested A and some values 
    // main.B -> {{a val} b val}

    fmt.Println("b.b ->", b.b)       // B's own value
    // b.b -> b val

    fmt.Println("b.A.a ->", b.A.a)   // B's nested value
    // b.a -> a val

    fmt.Println("b.a ->", b.a)       // B's nested value? or own value?
    // b.a -> a val
}

那么最后两行如何以及为何起作用？他们是一样的吗？我应该使用哪个？

Answer 1

它们是一样的。参见 the Go Spec on selectors :

For a value x of type T or *T where T is not a pointer or interface type, x.f denotes the field or method at the shallowest depth in T where there is such an f. If there is not exactly one f with shallowest depth, the selector expression is illegal.

请注意，如果类型 B 在相同深度嵌入具有相同字段的两个类型，则这意味着 b.a 是非法的:

type A1 struct{ a string }
type A2 struct{ a string }
type B struct {
    A1
    A2
}

// ...
b := B{A1{"a1"}, A2{"a2"}}
fmt.Println(b.a) // Error: ambiguous selector b.a

Playground :http://play.golang.org/p/PTqm-HzBDr .