构成特征时Scala类型不匹配
我试图计算一些我以后需要参考的类型 我试图通过将类型存储在类型成员中来实现这一点 下面是一个例子:构成特征时Scala类型不匹配,scala,generics,types,Scala,Generics,Types,我试图计算一些我以后需要参考的类型 我试图通过将类型存储在类型成员中来实现这一点 下面是一个例子: trait TypeClass[A] { def op(x: A): A } object TypeClass { implicit object FloatIsTypeClass extends TypeClass[Float] { override def op(x: Float) = x } implicit object DoubleI
trait TypeClass[A] {
def op(x: A): A
}
object TypeClass {
implicit object FloatIsTypeClass extends TypeClass[Float] {
override def op(x: Float) = x
}
implicit object DoubleIsTypeClass extends TypeClass[Double] {
override def op(x: Double) = x
}
}
object TraitBounds {
trait Types1 {
type Member1
val cls1: TypeClass[Member1]
}
class Types1Impl[A](implicit ev: TypeClass[A]) extends Types1 {
type Member1 = A
override val cls1 = ev
}
trait Types2 {
type Member2
val cls2: TypeClass[Member2]
}
class Types2Impl[A](implicit ev: TypeClass[A]) extends Types2 {
type Member2 = A
override val cls2 = ev
}
trait AllTypes extends Types1 with Types2
def mk(x: Int): AllTypes = {
import TypeClass._
val (instance1, instance2) =
if (x == 1) {
(new Types1Impl[Float](), new Types2Impl[Double]())
} else {
(new Types1Impl[Double](), new Types2Impl[Float]())
}
new AllTypes {
override type Member1 = instance1.Member1
override val cls1 = instance1.cls1
override type Member2 = instance2.Member2
override val cls2 = instance2.cls2
}
}
def main(args: Array[String]): Unit = {
val in = mk(1)
println(in)
}
}
我得到以下错误:
Error:(54, 43) type mismatch;
found : TypeClass[_1]
required: TypeClass[this.Member1]
(which expands to) TypeClass[_1]
override val cls1 = instance1.cls1
在我看来,我表达的东西应该是可以接受的,但出于某种原因,编译器不理解我试图做什么(或者可能我错了)
为什么会出现类型错误?有解决方法吗?可能存在一些关于类型系统的错误,尤其是在这行
val(instance1,instance2)=
中,因为在的一个分支中,如果instance1
的类型为Types1Impl[Float]
,而在另一个分支中的类型为Types1Impl[Double]
,它可能被推断为类型Types1Impl[AnyVal]
,也许这就是问题的原因,但我对编译器了解不多,不知道确切的原因
不过,我对您的代码进行了一点重构,它对我来说很有用
trait TypeClass[A] {
def op(x: A): A
}
object TypeClass {
implicit val FloatIsTypeClass: TypeClass[Float] = new TypeClass[Float] {
override def op(x: Float): Float = x
}
implicit val DoubleIsTypeClass: TypeClass[Double] = new TypeClass[Double] {
override def op(x: Double): Double = x
}
}
object TraitBounds {
trait Types1 {
type Member1
val cls1: TypeClass[Member1]
}
object Types1 {
private class Types1Impl[A](implicit ev: TypeClass[A]) extends Types1 {
override type Member1 = A
override val cls1 = ev
}
def apply[A: TypeClass]: Types1 = new Types1Impl[A]
}
trait Types2 {
type Member2
val cls2: TypeClass[Member2]
}
object Types2 {
private class Types2Impl[A](implicit ev: TypeClass[A]) extends Types2 {
override type Member2 = A
override val cls2 = ev
}
def apply[A: TypeClass]: Types2 = new Types2Impl[A]
}
trait AllTypes extends Types1 with Types2
object AllTypes {
def fromTypes(t1: Types1, t2: Types2): AllTypes = new AllTypes {
override type Member1 = t1.Member1
override val cls1 = t1.cls1
override type Member2 = t2.Member2
override val cls2 = t2.cls2
}
}
def mk(x: Int): AllTypes =
if (x == 1) {
AllTypes.fromTypes(Types1[Float], Types2[Double])
} else {
AllTypes.fromTypes(Types1[Double], Types2[Float])
}
def main(args: Array[String]): Unit = {
val in: AllTypes = mk(1)
println(in)
}
}
注意,与隐式对象相比,总是更喜欢带有特定类型签名的隐式VAL
和defs
,它们往往会弄乱类型系统,因为对象的类型是ThatObjectName.type
另外,将您的实现隐藏在工厂构造函数后面,将它们的类型隐藏到父trait
可能存在一些关于类型系统的错误,特别是在这一行val(instance1,instance2)=
,由于在的一个分支中,如果实例1
的类型为Types1Impl[Float]
,而在另一个分支中的类型为Types1Impl[Double]
,则可以推断为类型Types1Impl[AnyVal]
,可能这就是问题的原因,但我对编译器了解不多,不知道确切的原因
不过,我对您的代码进行了一点重构,它对我来说很有用
trait TypeClass[A] {
def op(x: A): A
}
object TypeClass {
implicit val FloatIsTypeClass: TypeClass[Float] = new TypeClass[Float] {
override def op(x: Float): Float = x
}
implicit val DoubleIsTypeClass: TypeClass[Double] = new TypeClass[Double] {
override def op(x: Double): Double = x
}
}
object TraitBounds {
trait Types1 {
type Member1
val cls1: TypeClass[Member1]
}
object Types1 {
private class Types1Impl[A](implicit ev: TypeClass[A]) extends Types1 {
override type Member1 = A
override val cls1 = ev
}
def apply[A: TypeClass]: Types1 = new Types1Impl[A]
}
trait Types2 {
type Member2
val cls2: TypeClass[Member2]
}
object Types2 {
private class Types2Impl[A](implicit ev: TypeClass[A]) extends Types2 {
override type Member2 = A
override val cls2 = ev
}
def apply[A: TypeClass]: Types2 = new Types2Impl[A]
}
trait AllTypes extends Types1 with Types2
object AllTypes {
def fromTypes(t1: Types1, t2: Types2): AllTypes = new AllTypes {
override type Member1 = t1.Member1
override val cls1 = t1.cls1
override type Member2 = t2.Member2
override val cls2 = t2.cls2
}
}
def mk(x: Int): AllTypes =
if (x == 1) {
AllTypes.fromTypes(Types1[Float], Types2[Double])
} else {
AllTypes.fromTypes(Types1[Double], Types2[Float])
}
def main(args: Array[String]): Unit = {
val in: AllTypes = mk(1)
println(in)
}
}
注意,与隐式对象相比,总是更喜欢带有特定类型签名的隐式VAL
和defs
,它们往往会弄乱类型系统,因为对象的类型是ThatObjectName.type
另外,将实现隐藏在工厂构造函数后面,将它们的类型隐藏到父trait