Go : How to use interfaces in maps and slices

I need a map of an interface because I want to be able to run a function that can use concrete implementations of either interface without caring about the "extra" stuff that those structs can do.

I've read https://jordanorelli.com/post/32665860244/how-to-use-interfaces-in-go which has a really great explanation of pointers and interfaces, but I still don't know how to accomplish what I want in practice.

I am trying the below code:

https://play.golang.com/p/nRH2IyK7t9F

package main

import (
	"fmt"
)

type IExample interface {
	GetName() string
}

type Concrete struct {
	Name string
}

func (c *Concrete) GetName() string {
	return c.Name
}

func main() {
    // in my real application this is a slice returned from Gorm orm
	var s = []Concrete{
		Concrete{Name: "one"},
		Concrete{Name: "two"},
	}

	foo := make(map[string]IExample)
	bar := []IExample{}

	for _, c := range s {
		foo[c.Name] = &c
		bar = append(bar, &c)
		fmt.Printf("Set key [%s]\r\n", c.Name)
	}

	for name, element := range foo {
		fmt.Printf("key: [%s] has element [%s]\r\n", name, element.GetName())
	}
	for name, element := range bar {
		fmt.Printf("key: [%d] has element [%s]\r\n", name, element.GetName())
	}

}

This outputs:

Set key [one]
Set key [two]
key: [one] has element [two]
key: [two] has element [two]
key: [0] has element [two]
key: [1] has element [two]

What I really want is for element one to be in key "one".

I imagine that the problem is happening because of the assignment using a reference foo[c.Name] = &c. I need this because otherwise I get the error "cannot use c (variable of type Concrete) as IExample value in assignment: Concrete does not implement IExample (method GetName has pointer receiver)"

After reading https://dusted.codes/using-go-generics-to-pass-struct-slices-for-interface-slices I wondered if the problem could be solved using generics, but I can't work out how to implement that.

type ExampleMap map[string]IExample

func (e *ExampleMap) add[T IExample](id string item T) {
	e[id] = item
}
// syntax error: method must have no type parameters

How can I get this map to contain the correct elements?

What you are doing is correct. You just put the wrong thing into the map:

for i,c := range s {
        foo[c.Name] = &s[i]
        bar = append(bar, &s[i])
        fmt.Printf("Set key [%s]\r\n", c.Name)
    }

The loop variable is rewritten at each iteration, so when you add &c to the map and to the slice, the pointer you add is the address of c, which is overwritten at each iteration.