我有以下想法:
trait Generator[A] {
def generate: Stream[A]
// (1) If A <: Int
def +(other: Generator[Int]): Generator[Int] = (
CustomGeneratorInt(
(this.asInstanceOf[Generator[Int]].generate, other.generate)
.zipped
.map(_ + _))
)
// (2) If A <: Boolean
def &&(other: Generator[Boolean]): Generator[Boolean] = ...
}
case class CustomGeneratorInt(val generate: Stream[Int]) extends Generator[Int]
case class ConstantInt(i: Int) extends Generator[Int] { def generate = Stream(i) }
case class ConstantBool(i: Boolean) extends Generator[Boolean] { def generate = Stream(i) }
case class GeneratorRandomInt(i: Int) extends Generator[Int] { def generate = ... }
ConstantInt(1) + ConstantInt(2) // (3) ok
ConstantBool(true) && ConstantBool(false) // (4) ok
ConstantInt(1) + ConstantBool(false) // (5)
ConstantBool(true) + ConstantInt(1) // (6) compiles but it's bad
ConstantBool(true) && ConstantInt(1) // (7)
ConstantInt(1) && ConstantBool(true) // (8) compiles but it's bad
如果 (1) 和 (2) 没有在正确的方案中应用,我希望 (1) 和 (2) 引发编译器异常。例如,虽然 (6) 和 (8) 当前可以编译,但它们不应该。 (5) 和 (7) 已经不编译了。
如何指定要应用这些方法的类型条件?
最佳答案
您可以使用通用类型约束(请参阅 this answer )来实现您想要的:
trait Generator[A] {
def generate: Stream[A]
def +(other: Generator[A])(implicit evidence: A =:= Int): Generator[Int] = ???
def &&(other: Generator[A])(implicit evidence: A =:= Boolean): Generator[Boolean] = ???
}
case class GeneratorInt(i: Int) extends Generator[Int] { def generate = Stream(i) }
case class GeneratorBool(i: Boolean) extends Generator[Boolean] { def generate = Stream(i) }
GeneratorInt(1) + GeneratorInt(2) // (3) ok
GeneratorBool(true) && GeneratorBool(false) // (4) ok
GeneratorInt(1) + GeneratorBool(false) // (5) type mismatch
GeneratorBool(true) + GeneratorInt(1) // (6) type mismatch
GeneratorBool(true) && GeneratorInt(1) // (7) type mismatch
GeneratorInt(1) && GeneratorBool(true) // (8) type mismatch
关于Scala:如何在特征中添加依赖于类型的方法?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/16769079/