Golang return map[string]interface{} returning variable struct

I need a big table of structs and I need to work off the struct returned.

package main

import (
    "fmt"
)

var factory map[string]interface{} = map[string]interface{}{
	"Date":                                 Date{},
	"DateTime":                             DateTime{},
}

type Date struct {
	year  int //xsd:int Year (e.g., 2009)
	month int //xsd:int Month (1..12)
	day   int //xsd:int Day number
}

func( d *Date ) Init(){
	d.year = 2009
	d.month = 1
	d.day = 1
}

type DateTime struct {
	date       Date   //Date
	hour       int    //xsd:int
	minute     int    //xsd:int
	second     int    //xsd:int
	timeZoneID string //xsd:string
}

func( d *DateTime ) Init(){
	d.hour = 0
	d.minute = 0
	d.second = 0
	
}

func main() {
	obj := factory["Date"]
	obj.Init()
	fmt.Println( obj ) 
	
}

Go Playground
but I get the error obj.Init undefined (type interface {} is interface with no methods) Is there a way to do this?

Basically, you need to tell the compiler that all your types (instances in the map) will always have an Init method. For that you declare an interface with the Init method and build a map of that interface.
Since your receivers work on a pointer *xxx, you need to add the pointers of the objects to the map (not the objects themselves) by adding & in front of them.

package main

import (
	"fmt"
)

type initializer interface {
	Init()
}

var factory map[string]initializer = map[string]initializer{
	"Date":     &Date{},
	"DateTime": &DateTime{},
}

type Date struct {
	year  int //xsd:int Year (e.g., 2009)
	month int //xsd:int Month (1..12)
	day   int //xsd:int Day number
}

func (d *Date) Init() {
	d.year = 2009
	d.month = 1
	d.day = 1
}

type DateTime struct {
	date       Date   //Date
	hour       int    //xsd:int
	minute     int    //xsd:int
	second     int    //xsd:int
	timeZoneID string //xsd:string
}

func (d *DateTime) Init() {
	d.hour = 0
	d.minute = 0
	d.second = 0

}

func main() {
	obj := factory["Date"]
	obj.Init()
	fmt.Println(obj)

}