Scala 案例类的重载构造函数？
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Overload constructor for Scala's Case Classes?
提问by Felix
In Scala 2.8 is there a way to overload constructors of a case class?
在 Scala 2.8 中有没有办法重载 case 类的构造函数？
If yes, please put a snippet to explain, if not, please explain why?
如果是，请放一个片段来解释，如果不是，请解释为什么？
回答by retronym
Overloading constructors isn't special for case classes:
重载构造函数对于 case 类并不特殊：
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 applymethod in the companion object, which is called when you omit new.
但是，您可能还想重载apply伴随对象中的方法，当您省略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.
在 Scala 2.8 中，通常可以使用命名参数和默认参数来代替重载。
case class Baz(bar: Int, baz: Int = 0)
new Baz(1)
Baz(1)
回答by Lukas Rytz
You can define an overloaded constructor the usual way, but to invoke it you have to use the "new" keyword.
您可以按照通常的方式定义重载构造函数，但要调用它，您必须使用“new”关键字。
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)
