Scala：如何在trait中添加依赖于类型的方法？
发布时间：2020-12-16 18:22:21 所属栏目：安全 来源：网络整理
导读：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
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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
如果它们没有应用于正确的方案,我希望(1)和(2)引发编译器异常.例如,虽然(6)和(8)目前编译,但他们不应该编译. (5)和(7)已经不编译了. 解决方法
您可以使用通用类型约束(请参阅
this answer)来实现您的目标：
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
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