var doTest : boolean = true; 　　
var dateFn : String; 　　
if(doTest) 　　
    dateFn = "Date(1971,3,8)"; 　　
  else 　　
    dateFn = "Date()"; 　　
var mydate : Date; 　　
eval("mydate = new "+dateFn+";"); 　　
print(mydate);

麻烦解答一下eval("mydate = new "+dateFn+";");