Interfaces in Golang

What are Interfaces in Golang?

An interface type is defined as a set of method signatures.

Syntax: type  var_name  interface  {}

An interface describes behaviors. Hence you put methods(i.e. behaviors) inside it.Let me take an example to explain this. Let chef be an interface who has methods 1) Cut and 2) Cook. We can also say that anyone who can 1) Cut and 2) Cook is a Chef. In order to explain the above statement in more detail here is one more example: In this example we take a structure called anyPerson. If anyPerson implements 1) Cut and 2) Cook; then anyPerson is a chef :D

package main

import (
	"fmt"
)

type chef interface {
	cut()
	cook()
}

type anyPerson struct {
}

func (a anyPerson) cut() {
	fmt.Println("anyPerson can cut... chop chop chop")

}

func (a anyPerson) cook() {
	fmt.Println("anyPerson can cook...sizzle sizzle pop!")

}

func main() {
	aP := anyPerson{}
	aP.cut()
	aP.cook()
}

Another example with a slight variation is here!

Interfaces are implemented implicitly. A type implements an interface by implementing its methods or we can also say that any structure that implements all the behaviors(i.e. methods) of an interface becomes an interface.

type Cruder interface {
        Create(conn *dbConnection, name string, amount int) (*models.SuccessStruct, error)
	Read(conn *dbConnection) (*[]models.Customer, error) 
	Update(conn *dbConnection, n string, amt int, id int) (*models.SuccessStruct, error)
	Delete(conn *dbConnection, id int) (*models.SuccessStruct, error)
}



type myStore struct {
}

//Now, we will make myStore an interface.

func (m myStore) Create(conn *dbConnection, name string, amount int) error {
	fmt.Println("This is the Create Method")
	}
	return nil
}

func (m myStore) Read(conn *dbConnection, name string, amount int) error {
	fmt.Println("This is the Read Method")
	}
	return nil
}

func (m myStore) Update(conn *dbConnection, name string, amount int) error {
	fmt.Println("This is the Update Method")
	}
	return nil
}

func (m myStore) Delete(conn *dbConnection, name string, amount int) error {
	fmt.Println("This is the Delete Method")
	}
	return nil
}

Why do we use Interfaces in Golang?

I have listed a few advantages of interfaces in Go:

We can write shorter programs which are easier to understand.
They help us to make great APIs.
Go methods can accept empty interfaces too. This means that the input parameter of a function can accept any type and perform the the subsequent operations based on the type given as input.
Interfaces are satisfied implicitly, so you can write interfaces for code that you don't own. For example, if your database has a JSON data stored in form of a string(i.e varchar) and we need to store that value inside a user defined structure. We generally use the Scan() function in order to read values. Unfortunately, Scan() function has only been implemented for primitive data types so we cannot use it for user defined structures. Damn what to do now? Interfaces come to the rescue here. We just implement Scan() with the structure.

(u userDefinedStructure) DB.Scan() {
// Unmarshall the data into 'u'
}

A few links I referred to while writing this article: