Scala 中级早期初始化器

Question

scala 中有没有办法使用中间早期初始化程序？

这是我要编译的内容：

trait A { val valueA: Int = 0 }
trait B { 
  val valueB: Int 
  println(valueB)
}


class C extends A with { val valueB = valueA } with B

编辑：对路易斯问题的回应

借助 scalatest，可以使用特征构造函数来组织固定装置。我想参数化一个子夹具并使用超夹具中的字段提前初始化。

这是另一个与真实的最严重案例更相关的示例：

class Test extends FreeSpec {
  trait CommonFixture {
    val commonCaseValue: Int = 1
  }
  abstract trait SpecialCaseFixture {
    val specialCaseValue: Int
  }

  "special case test #1" in new CommonCaseFixture with { val specialCaseValue = commonCaseValue } with SpecialCaseFixture {
    // all fixtures fields are accessible here
  }
}

Answer 1

可能有其他方法可以编写测试而不必使用早期初始化程序（已弃用），例如以下可能会提供一些想法

class FixturesSpec extends FlatSpec with Matchers {
  case class FixtureA(x: Int = 42)
  case class FixtureB(y: Int = -11)

  trait CommonFixture {
    val commonCaseValue: Int = 1
  }
  trait SpecialCaseFixture {
    val specialCaseValue: Int
  }

  "traits" should "be fixtures" in new SpecialCaseFixture with CommonFixture  {
    override val specialCaseValue = commonCaseValue
    specialCaseValue should be (1)
  }

  "case classes" should "be fixtures" in new FixtureA(FixtureB().y)  {
    x should be (-11)
  }
}

Answer 2

只需用 lazy val 覆盖它：

trait A { val valueA: Int = 100500 }
trait B {
  val valueB: Int
  println(valueB)
}
class C extends A with B { lazy val valueB = valueA } 
new C 
// prints 100500

Scala 中级早期初始化器

Scala intermediate early initializer

scala

traits

fixtures

scalatest