如何将未编组的 Golang 对象转换为指定变量的类型

Question

我想将各种对象编组到文件中，然后解组它们，并通过获取编组的变量的类型将它们转换回原始类型。关键是我想将未编组的对象转换为指定变量的类型，而不指定类型。

简短的伪代码：

// Marshal this

item := Book{"The Myth of Sisyphus", "Albert Camus"}

// Then unmarshal and convert to the type of the item variable.

itemType := reflect.TypeOf(item)

newItem itemType = unmarshalledItem.(itemType)  // This is the problem.

fmt.Println("Unmarshalled is:", reflect.TypeOf(newItem)) // Should print *main.Book

完整代码：

package main

import (

    "encoding/json"

    "fmt"

    "io/ioutil"

    "os"

    "reflect"

)

type Book struct {

    Title  string

    Author string

}

func main() {

    // Create objects to marshal.

    book := Book{"The Myth of Sisyphus", "Albert Camus"}

    box := make(map[string]interface{})

    box["The Myth of Sisyphus"] = &book

    itemType := reflect.TypeOf(box["The Myth of Sisyphus"])

    fmt.Println("Book is:", itemType)

    // Marshal objects to file.

    err := Write(&book)

    if err != nil {

        fmt.Println("Unable to save store.", err)

        return

    }

    // Unmarshal objects from file.

    untyped := make(map[string]interface{})

    bytes, err := ioutil.ReadFile("store.txt")

    if err != nil {

        fmt.Println("Unable to load store.", err)

        return

    }

    err = json.Unmarshal(bytes, &untyped)

    if err != nil {

        fmt.Println("Err in store unmarshal.", err)

        return

    }

    // Get Title property of unmarshalled object,

    // and use that to get variable type from box map.

    for k, v := range untyped {

        if k == "Title" {

            itemTitle := v.(string)

            fmt.Println("Cast item having title:", itemTitle)

            targetType := reflect.TypeOf(box[itemTitle])

            fmt.Println("Type to cast to is:", targetType)

            // Convert untyped to targetType.

            // This is the problem.

            typed targetType = untyped.(targetType)

            fmt.Println("Unmarshalled is:", reflect.TypeOf(typed)) // Should print *main.Book

        }

    }

}