Function/Method Overloading in Golang (Alternatives/Workaround)

Function/Method Overloading means that that the same function/method name can be used with a different number and types of parameters

See this post for difference between function and method in Go – https://golangbyexample.com/difference-between-method-function-go

Eg.

func X()
func X(name string)
func X(name, address string)
func X(name string, age int)

Go doesn’t support method/function overloading. See this faq for the reason https://golang.org/doc/faq#overloading

According to the above faq things are simpler without it.

We can workaround Method/Function overloading in GO using

• Variadic Function – A Variadic Function is a function that accepts a variable number of arguments
• Empty Interface – It is an interface without any methods.

There are two cases for Method/Function Overloading

1.Different number of parameters but of the same type:

Above case can easily be handled using variadic functions. Notice in below code the parameters are of one type i.e. int.

package main

import "fmt"

func main() {
    fmt.Println(add(1, 2))
    fmt.Println(add(1, 2, 3))
    fmt.Println(add(1, 2, 3, 4))
}

func add(numbers ...int) int {
    sum := 0
    for _, num := range numbers {
        sum += num
    }
    return sum

Output:

3
6
10

2.Different number of parameters and of different types

This case can be handled using both variadic function and empty interface

package main

import "fmt"

func main() {
    handle(1, "abc")
    handle("abc", "xyz", 3)
    handle(1, 2, 3, 4)
}

func handle(params ...interface{}) {
    fmt.Println("Handle func called with parameters:")
    for _, param := range params {
        fmt.Printf("%v\n", param)
    }
}

Output:

Handle func called with parameters:
1
abc
Handle func called with parameters:
abc
xyz
3
Handle func called with parameters:
1
2
3
4

We can also use a switch case to get the exact parameters and use them accordingly. See the below example.

package main

import "fmt"

type person struct {
    name   string
    gender string
    age    int
}

func main() {
    err := addPerson("Tina", "Female", 20)
    if err != nil {
        fmt.Println("PersonAdd Error: " + err.Error())
    }
    
    err = addPerson("John", "Male")
    if err != nil {
        fmt.Println("PersonAdd Error: " + err.Error())
    }
     
    err = addPerson("Wick", 2, 3)
    if err != nil {
        fmt.Println("PersonAdd Error: " + err.Error())
    }
}

func addPerson(args ...interface{}) error {
    if len(args) > 3 {
        return fmt.Errorf("Wront number of arguments passed")
    }
    p := &person{}
    //0 is name
    //1 is gender
    //2 is age
    for i, arg := range args {
        switch i {
        case 0: // name
            name, ok := arg.(string)
            if !ok {
                return fmt.Errorf("Name is not passed as string")
            }
            p.name = name
        case 1:
            gender, ok := arg.(string)
            if !ok {
                return fmt.Errorf("Gender is not passed as string")
            }
            p.gender = gender
        case 2:
            age, ok := arg.(int)
            if !ok {
                return fmt.Errorf("Age is not passed as int")
            }
            p.age = age
        default:
            return fmt.Errorf("Wrong parametes passed")
        }
    }
    fmt.Printf("Person struct is %+v\n", p)
    return nil
}

Note: Wherever the arg is not passed it is substituted as default.

Output:

Person struct is &{name:Tina gender:Female age:20}
Person struct is &{name:John gender:Male age:0}
PersonAdd Error: Gender is not passed as string