Simple demonstration of generics-like features in Go.

README.md

POLYMORPHISM AND GENERICS IN GO

Lately, Go has been getting a lot of flack for its lack of generics and parametric polymorphism. Whereas it doesn't have a specific language feature called "generics", generic type operations are very simple to implement. Here is a simple implementation of a generic collection type in Go demonstrating how it's done. Essentially, the type interface{} acts as a placeholder for any type. By making use of the empty interface, you can pass any type to a function much like you can in dynamically-typed languages.

Edit: Thanks to https://gist.github.com/mfenniak and https://gist.github.com/dominikh for pointing out that the add() function was equivalent to go's built-in append()

generics.go

package main

import (
	"fmt"
	"reflect"
)

type CustomCollection struct {
	myElements []interface{}
}

func (c *CustomCollection) init() {
	c.myElements = nil
}

func (c *CustomCollection) add(element interface{}) {
	c.myElements = append(c.myElements, element)
}

func main() {
	stringCollection := []string{"one", "two", "three"}
	intCollection := []int{1, 2, 3}
	
	fmt.Println("The value of stringCollection is: ", stringCollection)
	fmt.Println("Now let's add it to a custom collection...")
	myCollection := new(CustomCollection)
	for _, v := range stringCollection {
		myCollection.add(v)
	}
	fmt.Println("The value of myCollection.myElements is: ", myCollection.myElements)
	fmt.Println("The type of myCollection.myElements is: ", reflect.TypeOf(myCollection.myElements))
	
	fmt.Println("Now let's do it with ints...")
	fmt.Print("The value of intCollection is: ", intCollection, "\n\n")
	fmt.Println("And now we're creating a custom collection with the same values...")
	myCollection = new(CustomCollection)
	for _, v := range intCollection {
		myCollection.add(v)
	}
	fmt.Println("The value of myCollection.myElements is: ", myCollection.myElements)
	fmt.Println("The type of myCollection.myElements is: ", reflect.TypeOf(myCollection.myElements))
}

Although this has nothing to do with your polymorphism, you should know your "add" method can be quite a bit simpler if you use the builtin append() method. "c.myElements = append(c.myElements, element)" would replace the entire function implementation, except possibly a nil check on c.myElements.

@mfenniak append works just fine on nil slices, due to the simple fact that capacity for nil slices is defined as 0.

(On a side note, it would also make add a lot more efficient)