Dotty cannot infer result type of generic Scala function taking type parameter trait with abstract type
来源： https://stackoverflow.com/questions/59101681/dotty-cannot-infer-result-type-of-generic-scala-function-taking-type-parameter-t
dotty
Dotty cannot infer result type of generic Scala function taking type parameter trait with abstract type
来源： https://stackoverflow.com/questions/59101681/dotty-cannot-infer-result-type-of-generic-scala-function-taking-type-parameter-t
Difference between union type LUB and supertype LUB
来源： https://stackoverflow.com/questions/62120884/difference-between-union-type-lub-and-supertype-lub
How to access parameter list of case class in a dotty macro
问题 I am trying to learn meta-programming in dotty. Specifically compile time code generation. I thought learning by building something would be a good approach. So I decided to make a CSV parser which will parse lines into case classes. I want to use dotty macros to generate decoders trait Decoder[T]{ def decode(str:String):Either[ParseError, T] } object Decoder { inline given stringDec as Decoder[String] = new Decoder[String] { override def decode(str: String): Either[ParseError, String] =
How does given keyword work in Scala 3 or dotty?
问题 I was going through Scala 3 documentation. They have introduced given keyword which is considered as the alternative of Scala 2 implicit . The code is here trait Ord[T] { def compare(x: T, y: T): Int def (x: T) < (y: T) = compare(x, y) < 0 def (x: T) > (y: T) = compare(x, y) > 0 } given intOrd: Ord[Int] { def compare(x: Int, y: Int) = if (x < y) -1 else if (x > y) +1 else 0 } given listOrd[T]: (ord: Ord[T]) => Ord[List[T]] { def compare(xs: List[T], ys: List[T]): Int = (xs, ys) match { case
How does given keyword work in Scala 3 or dotty?
问题 I was going through Scala 3 documentation. They have introduced given keyword which is considered as the alternative of Scala 2 implicit . The code is here trait Ord[T] { def compare(x: T, y: T): Int def (x: T) < (y: T) = compare(x, y) < 0 def (x: T) > (y: T) = compare(x, y) > 0 } given intOrd: Ord[Int] { def compare(x: Int, y: Int) = if (x < y) -1 else if (x > y) +1 else 0 } given listOrd[T]: (ord: Ord[T]) => Ord[List[T]] { def compare(xs: List[T], ys: List[T]): Int = (xs, ys) match { case
How to use given in Dotty?
问题 I was looking at Dotty docs under Contextual Abstractions page and I saw the Given Instances . Given instances (or, simply, "givens") define "canonical" values of certain types that serve for synthesizing arguments to given clauses. Example: trait Ord[T] { def compare(x: T, y: T): Int def (x: T) < (y: T) = compare(x, y) < 0 def (x: T) > (y: T) = compare(x, y) > 0 } given intOrd: Ord[Int] { def compare(x: Int, y: Int) = if (x < y) -1 else if (x > y) +1 else 0 } given listOrd[T]: (ord: Ord[T])
Type inference changes in Scala 3
问题 What changes in type inference will Scala 3 bring? Currently documentation simply states TODO. For example, Weak conformance Scala 2.13 scala> val i: Int = 42 val i: Int = 42 scala> val c: Char = 'a' val c: Char = a scala> List(i,c) val res0: List[Int] = List(42, 97) Scala 3 (dotty 0.24.0-RC1) scala> val i: Int = 42 val i: Int = 42 scala> val c: Char = 'a' val c: Char = a scala> List(i,c) val res0: List[AnyVal] = List(42, a) Equality Scala 2.13 scala> 42 == Some(42) ^ warning: comparing
Type inference changes in Scala 3
问题 What changes in type inference will Scala 3 bring? Currently documentation simply states TODO. For example, Weak conformance Scala 2.13 scala> val i: Int = 42 val i: Int = 42 scala> val c: Char = 'a' val c: Char = a scala> List(i,c) val res0: List[Int] = List(42, 97) Scala 3 (dotty 0.24.0-RC1) scala> val i: Int = 42 val i: Int = 42 scala> val c: Char = 'a' val c: Char = a scala> List(i,c) val res0: List[AnyVal] = List(42, a) Equality Scala 2.13 scala> 42 == Some(42) ^ warning: comparing
神奇的Scala Macro之旅（二）- 一个实例
优化的日志方式 package macros_demo import scala.language.experimental.macros import org.slf4j._ import scala.reflect.macros.whitebox. Context object Macros { implicit class LoggerEx( val logger: Logger) { def DEBUG( msg: String) : Unit = macro LogMacros. DEBUG1 def DEBUG( msg: String, exception: Exception) : Unit = macro LogMacros. DEBUG2 } object LogMacros { def DEBUG1( c: Context)( msg: c. Tree) : c. Tree = { import c.universe._ val pre = c.prefix q """ val x = $pre.logger if( x.isDebugEnabled ) x.debug($msg) """ } def DEBUG2(c : Context)( msg: c. Tree, exception: c. Tree) : c. Tree = { import c