Why do I get "Composite Literal Uses Unkeyed" error? - go

Question

I'm relatively new to Go and am working on building out a request decoder. The request comes in JSON format and we decode that to a map[string]interface{}. We then pass that object data in to be decoded to our own ProcessRequest struct. As I said I'm new so I am reusing some logic in similar parts of the code wrote by previous developers. Essentially we are checking the map for the necessary pieces and then setting and returning those. Can someone explain to me why I am getting the titled error? Would I have to set the items all the way down to base structs that no longer have any nested? Is there a better way to accomplish what I want? Here is the code and the related structs. It is highlighting the error on the return of the model.ProcessRequest. TYIA
type ProcessRequest struct {
RequestID string
Message *message.Message
Rule *Rule
Options *ProcessOptions
//TODO: Context EvaluatorContext
//TODO: Links
}
type Message struct {
ID int
Key string
Source string
Headers *HeaderSet
Categories *CategorySet
Properties *PropertySet
Streams *StreamSet
}
type RuleAction struct {
Name string
Expression map[string]interface{}
}
type RuleLink struct {
LinkID int
Condition map[string]interface{}
TargetRuleID int
}
type Rule struct {
Name string
Code string
Actions []RuleAction
Links []RuleLink
}
type object = map[string]interface{}
func DecodeProcessRequest(dataObject map[string]interface{}) (*model.ProcessRequest, error) {
var (
requestID string
message *message.Message
rule *model.Rule
options *model.ProcessOptions
err error
)
if reqIDSrc, ok := dataObject["requestId"]; ok {
if requestID, err = converter.ToString(reqIDSrc); err != nil {
return nil, errors.Wrapf(err, "Error reading property 'requestID'")
}
if requestID == "" {
return nil, errors.Errorf("Property 'requestID' is an empty string")
}
} else {
return nil, errors.Errorf("Missing required property 'requestID'")
}
if messageSrc, ok := dataObject["message"]; ok {
messageData, ok := messageSrc.(object)
if !ok {
return nil, errors.Errorf("Error reading property 'message': Value is not an object")
}
if message, err = DecodeMessage(messageData); err != nil {
return nil, errors.Wrapf(err, "Error reading property 'message'")
}
} else {
return nil, errors.Errorf("Missing required property 'message'")
}
if ruleSrc, ok := dataObject["rule"]; ok {
ruleObj, ok := ruleSrc.(object)
if !ok {
return nil, errors.Errorf("Error reading property 'rule': Value is not an object")
}
if rule, err = DecodeRule(ruleObj); err != nil {
return nil, errors.Wrapf(err, "Error reading 'rule' during decoding")
}
} else {
return nil, errors.Errorf("Missing required property 'requestID'")
}
// Parse plain object to a Message struct
return &model.ProcessRequest{
requestID,
message,
rule,
options,
}, nil
}

Answer 1

super said in this comment:
In general, the warning says that you should prefer to use the syntax ProcessRequest{ RequestID: requestID, ... }. Naming the keys instead of unkeyed values.
That worked for me. Also the explanation by kostix in this comment really helped.
Basically the idea is that if you use "unkeyed" way of defining struct literals, the meaning of your definitions depends on the way the fields of the underlying type are layed out. Now consider that your type has three fields of type string in a certain order. Now a couple of iterations down the road some programmer moves the second field to the 1st position—your literal will still compile but will end up defining a completely different value at runtime.