Return nil for a struct in Go

Question

I am connecting to a database, getting a row and then sending it back to the user. What I want to do though is have a return statement if I can't find that row or if I have an error.

Because I'm returning a struct I can't return nil and I get that error cannot use nil as type Item in return argument (Item is my struct)

I read online that if I use a pointer in the return statement and return *Item instead of Item then I'd be able to pass nil, when I try to create item := *Item{} I get the following error invalid indirect of Item literal (type Item)

I think there are a few solutions to this but I can't find any, what I really want to know is:

• How to return a pointer *Item instead of Item
• Is there another way to return nil for a struct?

Here's my code:

package main  import (     "fmt"     "github.com/aws/aws-lambda-go/lambda"    "github.com/aws/aws-sdk-go/aws"   "github.com/aws/aws-sdk-go/aws/session"   "github.com/aws/aws-sdk-go/service/dynamodb"   "github.com/aws/aws-sdk-go/service/dynamodb/dynamodbattribute" )  type Request struct {     Name string `json:"name"` }  type Item struct {   Name string `json:"name"`   Stock int `json:"stock"`   Price float64 `json:"price"` }  func Handler(request Request) (Item, error) {   sess, err := session.NewSession(&aws.Config{     Region: aws.String("us-west-2")},   )    // Create DynamoDB client   svc := dynamodb.New(sess)    result, err := svc.GetItem(&dynamodb.GetItemInput{     TableName: aws.String("Inventory"),     Key: map[string]*dynamodb.AttributeValue{       "name": {           S: aws.String(request.Name),       },     },   })    if err != nil {     fmt.Println(err.Error()) //     return nil, err   }    item := Item{}    err = dynamodbattribute.UnmarshalMap(result.Item, &item)    if err != nil {     panic(fmt.Sprintf("Failed to unmarshal Record, %v", err)) //     return nil, err   }    if item.Name == "" {       fmt.Println("Could not find item") //       return nil, nil   }    fmt.Println("Found item:")   fmt.Println("Name:  ", item.Name)   fmt.Println("Stock: ", item.Stock)   fmt.Println("Price:  ", item.Price)      return item, nil }  func main() {     lambda.Start(Handler) } 

Answer 1

You're assigning your item variable wrong. You said you tried item := *Item{}, whereas the way to create a pointer is either through the use of the new builtin, or to create a literal, and the address-of operator (&). The latter is the approach you'll most commonly see in golang. There are some cases where one would use new, but in this case, I'd go for the second approach:

So either:

item := &Item{} // or item := new(Item) 

Lastly, you can keep the code as-is, and just return a pointer at the end:

item := Item{} // some code here return &item, nil 

In case where you have to return an error, you can still have return nil, err

So putting everything together:

// return *Item instead of Item func Handler(request Request) (*Item, error) {    // your code here, eg:    item := Item{}    if err := dynamodbattribute.UnmarshalMap(result.Item, &item); err != nil {         return nil, err     }     return &item, nil } 

Alternatively, assign item as a pointer from the start

func Handler(request Request) (*Item, error) {    // your code here, eg:    item := &Item{}    if err := dynamodbattribute.UnmarshalMap(result.Item, item); err != nil {         return nil, err     }     return item, nil }