我从“Programming Scala”（第 2 版）一书中获取了这个 Scala quasiquote 示例
我收到此错误：https ://issues.scala-lang.org/browse/SI-9711
类型推断显示“Trees#Tree”，但类型推断已关闭。
import scala.reflect.api.Trees // For Trees#Tree (TreeNode)
import scala.reflect.macros.blackbox._
import scala.reflect.runtime.universe._ // To use Scala runtime reflection
/**
* Represents a macro invariant which is checked over the corresponding statements.
* Example:
* '''
* var mustBeHello = "Hello"
* invariant.execute(mustBeHello.equals("Hello")) {
* mustBeHello = "Goodbye"
* }
* // Throws invariant.InvariantFailure
* '''
*/
object invariant {
case class InvariantFailure(message: String) extends RuntimeException(message)
type SyntaxTree = scala.reflect.runtime.universe.Tree
type TreeNode = Trees#Tree // a syntax tree node that is in and of itself a tree
// These two methods are the same, but one is a function call and the other is a macro function call
def execute[RetType] (myPredicate: => Boolean)(block: => RetType): RetType = macro executeMacro
def executeMacro(context: Context)(myPredicate: SyntaxTree)(block: SyntaxTree) = {
val predicateString: String = showCode(myPredicate) // turn this predicate into a String
val q"..$statements" = block // make the block into a sequence of statements
val myStatements: Seq[TreeNode] = statements // the statements are a sequence of SyntaxTreeNodes, each node a little Tree
val invariantStatements = statements.flatMap { statement =>
// Error here:
val statementString: String = showCode(statement) /* Type mismatch, expected Tree, actual Trees#Tree */
val message: String =
s"FAILURE! $predicateString == false, for statement: " + statementString
val tif: SyntaxTree =
q"throw new metaprogramming.invariant.InvariantFailure($message)"
val predicate2: SyntaxTree =
q"if (false == $myPredicate) $tif"
val toReturn: List[SyntaxTree] =
List(q"{ val temp = $myStatements; $predicate2; temp };")
toReturn
}
val tif: SyntaxTree =
q"throw new metaprogramming.invariant.InvariantFailure($predicateString)"
val predicate: SyntaxTree =
q"if (false == $predicate) $tif"
val toReturn: SyntaxTree =
q"$predicate; ..$invariantStatements"
toReturn
}
}
^ 文档应该是不言自明的。类型推断是 Tree#Tree，但在示例代码中添加“:Tree#Tree”会导致编译出错：
[info] Compiling 2 Scala sources to /home/johnreed/sbtProjects/scala-trace-debug/target/scala-2.11/test-classes...
[error] /home/johnreed/sbtProjects/scala-trace-debug/src/test/scala/mataprogramming/invariant2.scala:30: type mismatch;
[error] found : TreeNode
error scala.reflect.api.Trees#Tree
[error] required: context.universe.Tree
[error] val exceptionMessage = s"FAILURE! $predicateAsString == false, for statement: " + showCode(statement)
我在 IntelliJ 中得到“类型不匹配，预期的树，实际的树#树”
