How to new an object with string in Golang

Question

How can I create an object when I am only having its type in string? I am looking for something like:

type someStruct struct {}

resultObject := new \"someStruct         


        

Answer 1

No...

Well, the answer is "yes, but" and it's a big but. There's no central registry of struct names in Go. You're not going to get a nice, clean standard library function called StructFromName(string) which is probably what you were hoping for.

Instead, you have to write that mapping yourself, something like

func StringToStruct(name string) (interface{}, error) {
    switch name {
    case "SomeStruct":
        return SomeStruct{}, nil
    case "SomeOtherStruct":
        return SomeOtherStruct{}, nil
    case "subpackage.Struct":
        return subpackage.Struct{}, nil
    default:
        return nil, fmt.Errorf("%s is not a known struct name", name)
    }
}

Answer 2

You can't directly do that in Go. The only thing close to that Go supports is reflect.New() in the reflection library, which accepts a reflect.Type object and creates a new value of its type.

Now, if you'd like to initialize a type instance by name, you can build a registry of types by name, and have a function that looks up the type by name and creates an instance. It's really ugly though and not very idiomatic to Go, but it can be done.

[EDIT] here's a working example of this. You still need to do type conversion manually:

package main

import (
    "fmt"
    "reflect"
)

//just a couple of structs
type Foo struct {
    Lol string
}

type Bar struct {
    Wut string
}


//this is the registry of types by name
var registry = map[string]reflect.Type{}

// add a type to the registry
func registerType(t reflect.Type) {
    name := t.Name()
    registry[name] = t
}


// create a new object by name, returning it as interface{}
func newByName(name string) interface{} {

    t, found := registry[name]
    if !found {
        panic("name not found!")
    }

    return reflect.New(t).Elem().Interface()
}

func main() {

    //register foo and bar
    registerType(reflect.TypeOf(Foo{}))
    registerType(reflect.TypeOf(Bar{}))

    //create new instances
    foo := newByName("Foo").(Foo)
    bar := newByName("Bar").(Bar)

    fmt.Println(reflect.TypeOf(foo), reflect.TypeOf(bar))
}

And again, I wouldn't advise you to do this, it's ugly and slow and non idiomatic