Golang: expected identifier on left side of :=syntax-CodePudding

I'm new to Golang and while trying to implement a simple client server model, I'm getting this error expected identifier on left side of :=syntax on line:

kvs.listener, err := net.Listen("tcp", ":9999")

Specifically the error is under kvs.

I'm not sure why this is happening. If I replace kvs.listener with a simple ln (i.e. no struct) the error go away. Can someone please help me in fixing this?

Code:

type keyValueServer struct {
    totalClients int
    listener     net.Listener
}

func New() KeyValueServer {
    server := &keyValueServer{
        totalClients: 0,
    }
    return server
}

func (kvs *keyValueServer) Start(port int) error {
    kvs.listener, err := net.Listen("tcp", ":9999")

    if err != nil {
        fmt.Printf("Couldn't listen on port 9999: %s\n", err)
        return nil
    }

    go setupConnection(kvs)

}

Thanks!

CodePudding user response：

:= is a short variable declaration. As its name says, it is to declare variables.

kvs.listener is not an identifier of a new variable you wish to declare, it's likely a field of an existing variable (or a variable of some package).

When you don't want a new variable, use simple assignment:

kvs.listener, err = net.Listen("tcp", ":9999")

If the err variable does not yet exist, you have to declare it prior:

var err error
kvs.listener, err = net.Listen("tcp", ":9999")