[英]Scala type arguments do not conform to type parameter bounds
我正在做一些我想概括的工作(一些行為在幾個類中完全重復,但針對不同的具體類型 [稱為 C,見下文]),為了能夠使用所有具體類型之間共有的那些接口的一些行為(聽起來非常抽象和籠統......解釋我的問題的最佳方法是查看代碼)。
我用類似的結構簡化了真實的代碼,只是為了演示這個問題
package playground
object Conformance {
trait S
trait G
trait R {
type ST <: S
type GT <: G
def getS: ST
def getG: GT
}
trait RT[SD <: S, GD <: G] extends R {
override type ST = SD
override type GT = GD
}
final case class ConcreteS() extends S
final case class ConcreteG() extends G
final class C1 extends RT[ConcreteS, ConcreteG] {
override def getS: ConcreteS = ConcreteS()
override def getG: ConcreteG = ConcreteG()
}
//some different impl
final class C2 extends RT[ConcreteS, ConcreteG]{
override def getS: ConcreteS = ConcreteS()
override def getG: ConcreteG = ConcreteG()
}
//some different impl
final class C3 extends RT[ConcreteS, ConcreteG]{
override def getS: ConcreteS = ConcreteS()
override def getG: ConcreteG = ConcreteG()
}
//generic impl over W
trait GeneralizationOverW[C <: RT[S, G]] {
// With `<: RT[S, G]` restriction I know C is RT with some S and G I can use S and G behaviours
}
class W1 extends GeneralizationOverW[C1]
class W2 extends GeneralizationOverW[C2]
class W3 extends GeneralizationOverW[C3]
}
想象一下, C1,C2,C3
有不同的實現(由代碼生成),我嘗試使用不同的 C 和GeneralizationOverW
來概括 W
我試圖閱讀 Scala 規范中的復合類型,但無法弄清楚為什么會出現以下編譯錯誤以及如何修復它:
類型 arguments [playground.Conformance.C1] 不符合特征 GeneralizationOverW 的類型參數界限 [C <: playground.Conformance.RT[playground.Conformance.S,playground.Conformance.G]] class W1 擴展 GeneralizationOverW[C1]
編輯:建議后更新代碼:
package playground
object Conformance {
trait S
trait SS extends S
trait G
trait R {
type ST <: S
type GT <: G
def getS: ST
def getG: GT
}
trait RT[SD <: S, GD <: G] extends R {
override type ST = SD
override type GT = GD
}
final case class ConcreteS1() extends SS
final case class ConcreteS2() extends SS
final case class ConcreteS3() extends SS
final case class ConcreteG1() extends G
final case class ConcreteG2() extends G
final case class ConcreteG3() extends G
final class C1 extends RT[ConcreteS1, ConcreteG1] {
override def getS: ConcreteS1 = ConcreteS1()
override def getG: ConcreteG1 = ConcreteG1()
}
//some different impl
final class C2 extends RT[ConcreteS2, ConcreteG2]{
override def getS: ConcreteS2 = ConcreteS2()
override def getG: ConcreteG2 = ConcreteG2()
}
//some different impl
final class C3 extends RT[ConcreteS3, ConcreteG3]{
override def getS: ConcreteS3 = ConcreteS3()
override def getG: ConcreteG3 = ConcreteG3()
}
//generic impl over W
trait GeneralizationOverW[ST <: S,GT <: G , CON <: RT[ST, GT]] {
// With `<: RT[S, G]` restriction I know C is RT with some S and G I can use S and G behaviours
}
class W1 extends GeneralizationOverW[ConcreteS1,ConcreteG1,C1]
class W2 extends GeneralizationOverW[ConcreteS2,ConcreteG2,C2]
class W3 extends GeneralizationOverW[ConcreteS3,ConcreteG3,C3]
}
我認為它現在有效:)
我不確定這是您正在尋找的,但您可以嘗試:
trait GeneralizationOverW[S1 <: S, G1 <: G, C <: RT[S1, G1]] {
// With `<: RT[S, G]` restriction I know C is RT with some S and G I can use S and G behaviours
}
class W1 extends GeneralizationOverW[ConcreteS, ConcreteG, C1]
class W2 extends GeneralizationOverW[ConcreteS, ConcreteG, C2]
class W3 extends GeneralizationOverW[ConcreteS, ConcreteG, C3]
有幾件事正在發生:
trait GeneralizationOverW[C <: RT[S, G]] {
}
它預計此處傳遞的C
將准確擴展RT[S, G]
,使用S
和G
而不是它的子類型,因為RT
在兩個參數中都是不變的。
您可以通過添加+
使其成為協變的
trait RT[+SD <: S, +GD <: G] {
def getS: SD
def getG: GD
}
我刪除了extends R
因為路徑相關的類型ST
和GT
在這里定義:
trait R {
type ST <: S
type GT <: G
def getS: ST
def getG: GT
}
是不變的,不能成為協變的。 如果您放棄使用R
(您的示例根本沒有使用路徑相關類型),您可以創建一個有效代碼:
object Conformance {
trait S
trait G
trait RT[+SD <: S, +GD <: G] {
def getS: SD
def getG: GD
}
final case class ConcreteS() extends S
final case class ConcreteG() extends G
final class C1 extends RT[ConcreteS, ConcreteG] {
override def getS: ConcreteS = ConcreteS()
override def getG: ConcreteG = ConcreteG()
}
//some different impl
final class C2 extends RT[ConcreteS, ConcreteG]{
override def getS: ConcreteS = ConcreteS()
override def getG: ConcreteG = ConcreteG()
}
//some different impl
final class C3 extends RT[ConcreteS, ConcreteG]{
override def getS: ConcreteS = ConcreteS()
override def getG: ConcreteG = ConcreteG()
}
//generic impl over W
trait GeneralizationOverW[C <: RT[S, G]] {
// With `<: RT[S, G]` restriction I know C is RT with some S and G I can use S and G behaviours
}
class W1 extends GeneralizationOverW[C1]
class W2 extends GeneralizationOverW[C2]
class W3 extends GeneralizationOverW[C3]
}
但是,如果您確實需要這些依賴於路徑的類型,則應將硬編碼的S
和G
替換為 @TomerShetah 答案中的綁定參數。
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