scala 2.10.0 中高级类型的奇怪错误(适用于 scala 2.9.2) [英] Strange error with higher-kinded types in scala 2.10.0 (works with scala 2.9.2)

问题描述

此代码使用 Scala 2.9.2 编译:

This code compiles with Scala 2.9.2:

trait HK {
  type Rep[A]
  def unzip1[A, B, C[_]](ps: Rep[C[(A, B)]]): (Rep[C[A]], Rep[C[B]])
  def doUnzip1[A, B](ps: Rep[List[(A, B)]]) = unzip1(ps)
}

但是在 Scala 2.10.0 中它不会编译并出现以下错误(启用了更高级的语言功能):

But with Scala 2.10.0 it doesn't compile with the following error (higherKinded language feature is enabled):

[info] Compiling 1 Scala source to /home/klyuchnikov/code/hk/target/scala-2.10/classes...
[error] /home/klyuchnikov/code/hk/src/main/scala/HK.scala:6: type mismatch;
[error]  found   : HK.this.Rep[List[(A, B(in method doUnzip1))]]
[error]  required: HK.this.Rep[List[((A, B(in method doUnzip1)), B(in method unzip1))]]
[error]   def doUnzip1[A, B](ps: Rep[List[(A, B)]]) = unzip1(ps)

这里发生了什么?Scala 2.10 中高级类型有哪些变化?

What happens here? What was changes in higher-kinded types in Scala 2.10?

P.S. 如果我显式传递类型参数，则此代码将编译:

P.S. If I pass type parameters explicitly, then this code compiles:

trait HK {
  type Rep[A]
  def unzip1[A, B, C[_]](ps: Rep[C[(A, B)]]): (Rep[C[A]], Rep[C[B]])
  def doUnzip1[A, B](ps: Rep[List[(A, B)]]) = unzip1[A, B, List](ps)
}

推荐答案

看起来像一个错误，很可能:https://issues.scala-lang.org/browse/SI-5330

Looks like a bug, most likely: https://issues.scala-lang.org/browse/SI-5330

它应该在 Scala 2.10.1 中修复，如果你迫不及待，你可以尝试发布候选:http://www.scala-lang.org/2.10.1-RC3

It should be fixed in Scala 2.10.1, if you can't wait you may try release candidate: http://www.scala-lang.org/2.10.1-RC3

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