如何在golang中转换地图类型

Question

函数B返回类型map[T][]T如下:

type T interface{}
func B() map[T][]T {
  result := make(map[T][]T)
  return result
}

现在我有一个函数A像这样调用函数B:

func A() map[string][]string {
  res := B()
  return res.(map[string][]string) //I'm sure the type is map[string][]string, so I use assertion, but it doesn't works
}

那么，我怎么做这种覆盖类型的地图呢?

Answer 1

你不能。它们是完全不同的类型。您必须逐项复制并键入强制转换:http://play.golang.org/p/uhLPytbhpR

import "fmt"
type T interface{}
func B() map[T][]T {
    result := make(map[T][]T)
    return result
}
func A() map[string][]string {
    res := B()
    result := make(map[string][]string)
    for k,v := range res {
        key := k.(string)   
        value := make([]string, 0, len(res))
        for i := 0; i<len(value); i +=1 {
            value[i] = v[i].(string)
        }
        result[key]= value
    }
    return result
}
func main() {
    fmt.Println("Hello, playground", A())
}

Answer 2

另一种方法是返回T而不是map[T][]T play:

type T interface{}
func B() T {
    result := map[string][]string{
        "test": {"test", "test"},
    }
    return T(result)
}
func A() map[string][]string {
    res := B()
    if v, ok := res.(map[string][]string); ok {
        return v
    }
    return nil
}
func main() {
    fmt.Println("Hello, playground", A())
}

//编辑，转换函数:http://play.golang.org/p/cW_PNTqauV

func makeMap() map[T][]T {
    return map[T][]T{
        "test": {"test", "test"},
        "stuff": {"stuff", 1212, "stuff"},
        1: {10, 20},
    }
}
func convertMap(in map[T][]T) (out map[string][]string) {
    out = make(map[string][]string, len(in))
    for k, _ := range in {
        if ks, ok := k.(string); ok {
            v := in[k] // this way we won't use a copy in the for loop
            out[ks] = make([]string, 0, len(v))
            for i := range v {
                if vs, ok := v[i].(string); ok {
                    out[ks] = append(out[ks], vs)
                } else {
                    fmt.Printf("Error: %v (%T) is not a string.n", v[i], v[i])
                }
            }
        } else {
            fmt.Printf("Error: %v (%T) is not a string.n", k, k)
        }
    }
    return
}
func main() {
    fmt.Println(convertMap(makeMap()))
}