类构造函数声明......两种声明相同的方法？

Question

我希望对此声明之间的差异进行解释:

class Clazz(param1: String, param2: Integer)

还有这个:

class Clazz(param1: String)(param2: Integer)

第二个声明是否只影响实例化对象的方式,还是有更深层次的原因我不知道.

我想到的一个原因是多个可变长度的参数,例如:

class Clazz(param1: String*)(param2: Integer*)

还有其他人吗？

Answer 1

#1类型推断.它从左到右,按参数列表完成.

scala> class Foo[A](x: A, y: A => Unit)
defined class Foo

scala> new Foo(2, x => println(x))
<console>:24: error: missing parameter type
              new Foo(2, x => println(x))
                         ^

scala> class Foo[A](x: A)(y: A => Unit)
defined class Foo

scala> new Foo(2)(x => println(x))
res22: Foo[Int] = Foo@4dc1e4

#2隐式参数列表.

scala> class Foo[A](x: A)(implicit ord: scala.Ordering[A]) {
     |   def compare(y: A) = ord.compare(x, y)
     | }
defined class Foo

scala> new Foo(3)
res23: Foo[Int] = Foo@965701

scala> res23 compare 7
res24: Int = -1

scala> new Foo(new {})
<console>:24: error: No implicit Ordering defined for java.lang.Object.
              new Foo(new {})
              ^