How to use interface methods in main file in go?

I have an interface in the service package

databaseService.go

package service

    import "gitlab.com/xert/customerservice/internal/database/models"
    
    type CustomerdetailsServiceInterface interface {
    	// Remove deletes a user by user name from database.
    
    	
    	Add()
    }

Then I have another service file customerDetailsService.go,where i am implementing the interface methods

type CustomerdetailService struct {
}

func Add(ud *CustomerdetailService) {
	fmt.Println("hello")

}

Now when I am trying to use it my main.go

import (
	
	"gitlab.com/xert/customerservice/internal/database/service"
)

    func main() {
    
    	
    
    	service.CustomerdetailsServiceInterface.Add() // this is complaining too few arguments
    
    }

How to call the method like this, implement methods in other file?

You have not implemented CustomerdetailsServiceInterface in the first place. Following is the way you can implement it.

type CustomerdetailService struct {}

func (ud *CustomerdetailService) Add() {
    fmt.Println("hello")

}

See the following code, hope it will help you understanding interface in go.

package main
import ( 
	"fmt"
)

type CustomerdetailsServiceInterface interface {
	Add()
}

type CustomerdetailService struct{}

func (ud *CustomerdetailService) Add() {
	fmt.Println("hello")

}

type AnotherCustomerdetailService struct{}

func (ud *AnotherCustomerdetailService) Add() {
	fmt.Println("Modified Addition")

}

func main() {
	var x CustomerdetailsServiceInterface

	x = &CustomerdetailService{}
	x.Add()

	x = &AnotherCustomerdetailService{}
	x.Add()
}

You can not call a method directly on interface but you will need a variable with a type which implements the interface. In the above case it's CustomerdetailService which implements CustomerdetailsServiceInterface.