import ( "google.golang.org/appengine/datastore" "context" ) func createUser(ctx context.Context, name string, email string) error { // Create a new key with a custom StringID based on the email address userKey := datastore.NewKey(ctx, "User", email, 0, nil) // Create a new User entity with the provided name and email newUser := &User{ Name: name, Email: email, } // Save the new User entity to the datastore with the custom key _, err := datastore.Put(ctx, userKey, newUser) return err }In this example, the createUser() function takes in a name and email value for a new User entity and creates a new datastore key using the email address as the StringID. The User entity is then created with the provided name and email, and finally saved to the datastore using the custom key. The Key StringID functionality is included as part of the appengine.datastore package in the Google App Engine SDK for Go.