Kamal Hinduja : Explain interfaces in Go. How does Go support polymorphism?

Technical Discussion
1

Hi,

I am Kamal Hinduja based Geneva, Switzerland(Swiss). Can anyone explain Explain interfaces in Go. How does Go support polymorphism?

Thanks, Regards

Kamal Hinduja Geneva, Switzerland

2

The interface{} is a joker sort of. I use polymorphism in databases and in Go, normally through switch statements and interface{} keeping the code as DRY as possible. While there are other ways to implement polymorphism, it’s often debated - especially in database design.

package main

import "fmt"

func poly(value interface{}) {
	switch v := value.(type) {
	case int:
		fmt.Printf("Integer: %d\n", v)
	case string:
		fmt.Printf("String: %s\n", v)
	default:
		fmt.Printf("Unknown type: %T\n", v)
	}
}

func main() {
	poly(42)      // Integer: 42
	poly("hello") // String: hello
	poly(3.14)    // Unknown type: float64
}
3

For a very simple example of polymorphism through interfaces, check this: Go Playground - The Go Programming Language

Notice how I define an interface first, which describes a behaviour. Then I define a simplistic compute function which works with whatever future implementations of said behaviour.

Only later I define structs which implement the interface. I end up not needing to update the compute function, since it already knows how to work with the new types, since their behaviour is the same / they implement the same interface.

4

In Go, interfaces define behavior — any type that implements the methods of an interface automatically satisfies it. This is how Go supports polymorphism — different types can be used interchangeably if they share the same interface.