require

def this(name: String, age: Int) = {
  this()
  require(name != null && !name.isEmpty, "name")
  require(age > 0, "illegal age")
  Preconditions.checkArgument(name != null && !name.isEmpty, "name required")  // 使用 guava 工具类,这行编译不过... 改写为下两种调用方式可通过
// Preconditions.checkArgument(name != null && !name.isEmpty, "name required".asInstanceOf[Any])
// Preconditions.checkArgument(name != null && !name.isEmpty, "name required", null)
  setAge(age)
  setName(name)
}

什么鬼

  1. require
    • 函数签名: final def require(requirement: Boolean, message: => Any) ,注意第二个参数类型是一个函数
    • 以上栗子中调用了两次 require 函数,生成两个匿名对象...
  2. ambiguous reference to overloaded definition
    • 编译错误信息:
      Error:(44, 21) ambiguous reference to overloaded definition, both method checkArgument in object Preconditions of type (x$1: Boolean, x$2: String, x$3: Object*)Unit and method checkArgument in object Preconditions of type (x$1: Boolean, x$2: Any)Unit match argument types (Boolean,String) Preconditions.checkArgument(name != null && !name.isEmpty, "name required")
02-01 08:16