Set int64 value to *int64 pointer-CodePudding

I need map the struct to create a JSON structure. The collector_id attribute in JSON should be able to take null value or int value. I hace the follow code:

type purchaseInfo struct {
    CollectorID *int64 `json:"collector_id"`
}

func mapPurchaseInfo(collectorID int64) purchaseInfo {
    var collectorIDToSend *int64
    if collectorID < 0 {
        collectorIDToSend = nil
    } else {
        collectorIDToSend = collectorID
    }

    return purchaseInfo{
        CollectorID: collectorIDToSend,
    }
}

This code doesn't compile, the collectorID can't be assigned to collectorIDToSend. Is there a way to be able to do this?

Thanks!

CodePudding user response：

In the declaration of the mapPurchaseInfo function, to correctly assign the value passed in parameter to collectorIDToSend, the & operator must be used to retrieve the memory address of collectorID.
When constructing the purchaseInfo return variable, it is possible to put the fields of the structure directly as in the example.

type purchaseInfo struct {
        CollectorID *int64 `json:"collector_id"`
    }

    func mapPurchaseInfo(collectorID int64) purchaseInfo {
        var collectorIDToSend *int64
        if collectorID < 0 {
            collectorIDToSend = nil
        } else {
            collectorIDToSend = &collectorID
        }

        return purchaseInfo{
            CollectorID: collectorIDToSend,
        }
    }

CodePudding user response：

type purchaseInfo struct {
    CollectorID *int64 `json:"collector_id"`
}

func mapPurchaseInfo(collectorID *int64) purchaseInfo {
    if *collectorID < 0 {
        return purchaseInfo{CollectorID: nil}
    }
    return purchaseInfo{
        CollectorID: collectorID,
    }
}