Scala 案例类的重载构造函数？

You can define an overloaded constructor the usual way, but to invoke it you have to use the "new" keyword.

scala> case class A(i: Int) { def this(s: String) = this(s.toInt) }
defined class A


scala> A(1)
res0: A = A(1)


scala> A("2")
<console>:8: error: type mismatch;
found   : java.lang.String("2")
required: Int
A("2")
^


scala> new A("2")
res2: A = A(2)

Overloading constructors isn't special for case classes:

case class Foo(bar: Int, baz: Int) {
def this(bar: Int) = this(bar, 0)
}


new Foo(1, 2)
new Foo(1)

However, you may like to also overload the apply method in the companion object, which is called when you omit new.

object Foo {
def apply(bar: Int) = new Foo(bar)
}


Foo(1, 2)
Foo(1)

In Scala 2.8, named and default parameters can often be used instead of overloading.

case class Baz(bar: Int, baz: Int = 0)
new Baz(1)
Baz(1)