Interface example of retail

retail.go

type WarehouseItf interface {
  GetProduct(id int) (Product, error)
  InsertProduct(product Product) error
}

type Retail struct {
  warehouse WarehouseItf 
}

func (retail *Retail) GetMyProduct() ([]Product, error) {
  aProduct, err := retail.warehouse.GetProduct(1)
  if err != nil {
    return nil, err
  }
  return []Product{aProduct}, nil
}

func New(warehouse WarehouseItf) *Retail {
  return &Retail{warehouse} 
}