How to access the values of a message struct?

[jami]

Hi,
I'm currently using msg, err := pcapScanner.NextMessage() and I'm trying to access the values contained in the msg struct. When I try to access using msg.MessageType, I'm get an error:

./hello.go:69:51: msg.MessageType undefined (type iextp.Message has no field or method MessageType)

I know it has something to do with the inheritance between Message and other Message structs; what's the proper way of using this?

[Timothy Palpant]

Hi! You can use a type switch or type assertion to unwrap the iextp.Message interface into one of the concrete protocol types, then you can access the values. For example:

// Type switch
switch msg := msg.(type) {
case *tops.QuoteUpdateMessage:
    fmt.Printf("%v,%v,%v,%v,%v,%v\n",
        msg.Timestamp, msg.Symbol, msg.BidPrice,
        msg.BidSize, msg.AskPrice, msg.AskSize)
case *tops.TradeReportMessage:
    fmt.Printf("%v,%v,%v,%v\n", msg.Timestamp, msg.Symbol, msg.Price, msg.Size)
}

// Type assertion
if msg, ok := msg.(*tops.QuoteUpdateMessage); ok {
    fmt.Printf("Got a quote message: %v", msg.MessageType)
}

The different message types in the TOPS and DEEP feeds are are described in the IEX market data documentation, or you can refer to the GoDoc.

[Timothy Palpant]

Closing this, feel free to reopen if you have additional questions.