Scala default arguments of class constructor with expression using previous members
I want to create a class (or better case class) that will behave like this:
case class MyClass(n: Int, m: Int = 2 * n)
So it m
can have a default based on n
. But it seems that this is not possible, the scala says not found: value n
. The first idea is to write m: Int = -1
and mutate in the constructor if it's still -1, but it is val
. And now I have no other ideas.
Can anyone shed some light on what's possible here?
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You can explicitly provide a second factory:
case class MyClass(n: Int, m: Int)
object MyClass{
def apply(n: Int): MyClass = MyClass(n, 2 * n)
}
Unlike using 2 parameter lists as in @ om-nom-nom's answer, the case class is unaffected, and in particular, you can match the pattern as usual to extract both n
and m
.
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You must define a companion object:
scala> :paste
// Entering paste mode (ctrl-D to finish)
case class MyClass(n: Int, m: Int);
object MyClass {
def apply(n: Int) : MyClass = new MyClass(n, n * 2)
}
// Exiting paste mode, now interpreting.
defined class MyClass
defined module MyClass
scala> MyClass(12);
res4: MyClass = MyClass(12,24)
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