Actionscript 3 AS3套接字错误

AS3新手，我遇到以下错误：

1084:语法错误：冒号前应为rightbrace。连接：套接字：空，

var mc:Object = {
    Conn:Socket: null,
    Username:String: "fu",
};

function zSock(host:String = "70.32.72.134", port:String "70.32.72.134"):void {
    mc.Conn = new Socket(host, port);
    mc.Conn.addEventListener(Event.CONNECT, onConnect);
    mc.Conn.addEventListener(ProgressEvent.SOCKET_DATA, onData);
}

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不能严格限制对象的类型属性

var mc:Object = {
    Conn: null,
    Username: "fu",
};