Scala:路径依赖类型的等价性

Question

我如何解决两个与路径相关的类型的等价,我知道它们是相同但编译器没有？

使用Scala 2.10.0 M7我试图将AST从一个宇宙转换为另一个宇宙.

case class MacroBridge(context: Context) {
  def toMacroTree(tree: treehugger.forest.Tree): context.universe.Tree = ???
  def fromMacroTree(tree: context.universe.Tree): treehugger.forest.Tree = ???
}

在宏实现中,我可以将其用作:

val bridge = treehugger.MacroBridge(c)
def fromMacroTree(tree: c.universe.Tree): Tree = bridge.fromMacroTree(tree)

但是,这会导致编译器错误:

[error] /scalamacros-getting-started/library/Macros.scala:21: type mismatch;
[error]  found   : c.universe.Tree
[error]  required: bridge.context.universe.Tree
[error]  possible cause: missing arguments for method or constructor
[error]     def fromMacroTree(tree: c.universe.Tree): Tree = bridge.fromMacroTree(tree)

在上面的代码c显然是相同的值bridge.context,但也许是因为它是一个值类型检查器无法检查它.放置通用类型约束没有帮助:

def fromMacroTree[A](tree: A)(implicit ev: A =:= context.universe.Tree): Tree =

在宏中,这仍然导致错误:

[error] /scalamacros-getting-started/library/Macros.scala:21: Cannot prove that c.universe.Tree =:= bridge.context.universe.Tree.
[error]     def fromMacroTree(tree: c.universe.Tree): Tree = bridge.fromMacroTree(tree)

我需要访问权限,context.universe所以我可以访问其他依赖类型TermName.除了演员之外还有更好的解决方法吗？:

def fromMacroTree(tree: c.universe.Tree): Tree =
  bridge.fromMacroTree(tree.asInstanceOf[bridge.context.universe.Tree])

Answer 1

我可以做以下工作:

case class MacroBridge[C <: Context](context: C) {
  def fromMacroTree(tree: context.universe.Tree): context.universe.Tree = ???
}

trait MB {
  def meth(c: Context) {
    val bridge = MacroBridge[c.type](c)
    def fromMacroTree(tree: c.universe.Tree): c.universe.Tree =
      bridge.fromMacroTree(tree)
  }
}

前段时间我遇到了几乎相同的问题.