Compilation error: method call through an interface

Issue

I am learning go interfaces and trying to implement the below but vscode is showing me a compilation error, requesting help. What am I missing. Thank you.

package dataaccess

import (
  "../domain"
)

type IProductDataAccess interface {
    GetProducts() ([]*domain.Product, error)
    GetProduct(string) (*domain.Product, error)
}

var (
    ProductDataAccess IProductDataAccess
)

type productDAO struct{}

func init() {
    ProductDataAccess = new(productDAO)
}
func (p *productDAO) GetProduct(productID string) (*domain.Product, error) {
    return nil, nil
}
func (p *productDAO) GetProducts() ([]*domain.Product, error) {
    return nil, nil
}

Getting the following compilation errors in the editor when making the method calls on the IProductDataAccess from a component as shown below in a different package

not enough arguments in call to dataaccess.IProductDataAccess.GetProduct
have (string)
want (dataaccess.IProductDataAccess, string) (WrongArgCount)

not enough arguments in call to dataaccess.IProductDataAccess.GetProducts
have ()
want (dataaccess.IProductDataAccess)compiler (WrongArgCount)

package service

import (
    "../dataaccess"
    "../domain"
)

type IProductService interface {
    GetProducts() ([]*domain.Product, error)
    GetProduct(string) (*domain.Product, error)
}

var (
    ProductService IProductService
)

type productService struct{}

func init() {
    ProductService = new(productService)
}

func (p *productService) GetProduct(productID string) (*domain.Product, error) {
    product, err := dataaccess.IProductDataAccess.GetProduct(productID)
    if err != nil {
        return nil, err
    }
    return product, nil
}
func (p *productService) GetProducts() ([]*domain.Product, error) {
    products, err := dataaccess.IProductDataAccess.GetProducts()
    if err != nil {
        return nil, err
    }
    return products, nil
}

Solution

This line looks like it needs adjustment:

product, err := dataaccess.IProductDataAccess.GetProduct(productID)

dataaccess.IProductDataAccess is an interface, not an actual object to invoke a call on. dataaccess.ProductDataAccess is the singleton instance on that page that what you want to invoke.

I think you really want:

product, err := dataaccess.ProductDataAccess.GetProduct(productID)

Similarly for the GetProducts call:

products, err := dataaccess.ProductDataAccess.GetProducts()

Answered By – selbie

Answer Checked By – Robin (GoLangFix Admin)