scala

问题 I'm working with abstract types, and I'm wondering why this is invalid: class A {} class B extends A {} class X {type T = A} class Y extends X {override type T = B} Seeing as B <: A, why can't I assign B to T? I get this error: overriding type T in class X, which equals A; type T has incompatible type class Y extends X {override type T = B} Any help would be appreciated. 回答1: When you say this: class X {type T = A} you say: T is exactly A or T is an alias for A . It can't be anything else,

问题 I'm working with abstract types, and I'm wondering why this is invalid: class A {} class B extends A {} class X {type T = A} class Y extends X {override type T = B} Seeing as B <: A, why can't I assign B to T? I get this error: overriding type T in class X, which equals A; type T has incompatible type class Y extends X {override type T = B} Any help would be appreciated. 回答1: When you say this: class X {type T = A} you say: T is exactly A or T is an alias for A . It can't be anything else,

问题 I'm working with abstract types, and I'm wondering why this is invalid: class A {} class B extends A {} class X {type T = A} class Y extends X {override type T = B} Seeing as B <: A, why can't I assign B to T? I get this error: overriding type T in class X, which equals A; type T has incompatible type class Y extends X {override type T = B} Any help would be appreciated. 回答1: When you say this: class X {type T = A} you say: T is exactly A or T is an alias for A . It can't be anything else,

问题 I have written a method pythagoreanTriplets in scala using nested loops. As a newbie in scala, I am struggling with how can we do the same thing using recursion and use Lazy Evaluation for the returning list(List of tuples). Any help will be highly appreciated. P.S: The following method is working perfectly fine. // This method returns the list of all pythagorean triples whose components are // at most a given limit. Formula a^2 + b^2 = c^2 def pythagoreanTriplets(limit: Int): List[(Int, Int,

问题 I have written a method pythagoreanTriplets in scala using nested loops. As a newbie in scala, I am struggling with how can we do the same thing using recursion and use Lazy Evaluation for the returning list(List of tuples). Any help will be highly appreciated. P.S: The following method is working perfectly fine. // This method returns the list of all pythagorean triples whose components are // at most a given limit. Formula a^2 + b^2 = c^2 def pythagoreanTriplets(limit: Int): List[(Int, Int,

问题 I have a classic Encoder typeclass. trait Encoder[A] { def encode(a: A): String } I have two questions Question 1 : where does the divergence comes from : [error] … diverging implicit expansion for type sbopt.Test.Encoder[None.type] [error] starting with value stringEncoder in object Test [error] show(None) implicit val stringEncoder = new Encoder[String] { override def encode(a: String): String = a } implicit def optionEncoder[A: Encoder]: Encoder[Option[A]] = (a: Option[A]) => { val

问题 I have following function, that does not compile: private def save(pea: KStream[String, String]): Unit = { pea .groupByKey() .aggregate(() => """{folder: ""}""", (_: String, _: String, value: String) => value, EventStoreTopology.Store) } the error message is: [error] [VR](x$1: org.apache.kafka.streams.kstream.Initializer[VR], x$2: org.apache.kafka.streams.kstream.Aggregator[_ >: String, _ >: String, VR], x$3: org.apache.kafka.streams.processor.StateStoreSupplier[org.apache.kafka.streams.state

问题 I have a Flink application for click stream collection and processing. The application consists of Kafka as event source, a map function and a sink as image shown below: I want to enrich the incoming click stream data with user's IP location based on userIp field in raw event ingested from Kafka. a simplified slice of the CSV file as shown below start_ip,end_ip,country "1.1.1.1","100.100.100.100","United States of America" "100.100.100.101","200.200.200.200","China" I have made some

问题 import scala.reflect.runtime.universe._ val a: 42 = 42 val t: Type = typeOf[a.type] assert(getConstantType(t).get =:= typeOf[42]) def getConstantType(t: Type): Option[ConstantType] = ??? How could I generally implement getConstantType so that the above assertion passes? I assumed that something like this was possible since the assertion below passes: assert(t <:< typeOf[42]) t.widen goes too far as it return Int . I'm looking for something that returns Int(42) . 回答1: How about assert(t

问题 import scala.reflect.runtime.universe._ val a: 42 = 42 val t: Type = typeOf[a.type] assert(getConstantType(t).get =:= typeOf[42]) def getConstantType(t: Type): Option[ConstantType] = ??? How could I generally implement getConstantType so that the above assertion passes? I assumed that something like this was possible since the assertion below passes: assert(t <:< typeOf[42]) t.widen goes too far as it return Int . I'm looking for something that returns Int(42) . 回答1: How about assert(t