How do you create a new instance of a struct from its type at run time in Go?

Question

In Go, how do you create the instance of an object from its type at run time? I suppose you would also need to get the actual type of the object first too?

Answer 1

You don't need reflect and you can do this easy with factory pattern if they share the same interface:

package main

import (
    "fmt"
)

// Interface common for all classes
type MainInterface interface {
    GetId() string
}

// First type of object
type FirstType struct {
    Id string
}

func (ft *FirstType) GetId() string {
    return ft.Id
}

// FirstType factory
func InitializeFirstType(id string) MainInterface {
    return &FirstType{Id: id}
}


// Second type of object
type SecondType struct {
    Id string
}

func (st *SecondType) GetId() string {
    return st.Id
}

// SecondType factory
func InitializeSecondType(id string) MainInterface {
    return &SecondType{Id: id}
}


func main() {
    // Map of strings to factories
    classes := map[string]func(string) MainInterface{
        "first": InitializeFirstType,
        "second": InitializeSecondType,
    }

    // Create a new FirstType object with value of 10 using the factory
    newObject := classes["first"]("10")

    // Show that we have the object correctly created
    fmt.Printf("%v\n", newObject.GetId())


    // Create a new SecondType object with value of 20 using the factory
    newObject2 := classes["second"]("20")

    // Show that we have the object correctly created
    fmt.Printf("%v\n", newObject2.GetId())
}