斯卡拉宏注释 - 具有类型参数的案例类

Question

我想为向伴随对象添加方法的案例类编写一个简单的宏注释。问题在于新方法必须考虑带注释的案例类的类型参数。

下面是我需要传递

package my.macros 

import org.scalatest._ 

class DefaultApplyTest extends FlatSpec with Matchers { 

    @defaultApply case class Generic[A, B](a: A, b: B) 

    it should "define defaultApply method in companion object" in { 
    assert(Generic.defaultApply("str", 1) == Generic("str", 1)) 
    } 
} 

这里是我写我的理解是，当我尝试lift的做到这一点

package my.macros 

import scala.reflect.macros._ 
import scala.language.experimental.macros 
import scala.annotation.StaticAnnotation 

class defaultApply extends StaticAnnotation { 
    def macroTransform(annottees: Any*): Any = macro DefaultApply.impl 
} 

object DefaultApply { 

    def impl(c: blackbox.Context)(annottees: c.Expr[Any]*): c.Expr[Any] = { 
    import c.universe._ 

    def defaultApplyCompanion(classDecl: ClassDef) = { 
     val (name, typeParams, valueParams) = try { 
     val q"case class ${name: TypeName}[..${typeParams: Seq[TypeDef]}](..${valueParams: Seq[ValDef]}) extends ..$bases { ..$body }" = classDecl 
     (name, typeParams, valueParams) 
     } catch { 
     case e: MatchError => 
      c.warning(c.enclosingPosition, e.toString) 
      c.abort(c.enclosingPosition, "Annotation is only supported on case class") 
     } 

     val applyDef = q"""${name.toTermName}.apply[..$typeParams]""" 
     c.warning(c.enclosingPosition, showRaw(applyDef)) 

     q""" 
     object ${name.toTermName} { 
      def defaultApply: (..${valueParams.map(_.tpt)}) => $name[..$typeParams] = $applyDef 
     } 
     """ 
    } 

    def modifiedDeclaration(classDecl: ClassDef) = { 
     val compDecl = defaultApplyCompanion(classDecl) 

     c.Expr(q""" 
     $classDecl 
     $compDecl 
     """) 
    } 

    annottees.map(_.tree) match { 
     case (classDecl: ClassDef) :: Nil => modifiedDeclaration(classDecl) 
     case _ => c.abort(c.enclosingPosition, "Invalid annottee") 
    } 
    } 
} 

该问题的代码测试类型参数列表到结果语法树中，它们不会被识别为与原始树相同的类型参数。

那么我专注于是，宏观

val applyDef = q"""${name.toTermName}.apply[..$typeParams]""" 
    c.warning(c.enclosingPosition, showRaw(applyDef)) 

这部分原料语法树的发射是由于

TypeApply(Select(Ident(TermName("Generic")), TermName("apply")), List(TypeDef(Modifiers(PARAM), TypeName("A"), List(), TypeBoundsTree(EmptyTree, EmptyTree)), TypeDef(Modifiers(PARAM), TypeName("B"), List(), TypeBoundsTree(EmptyTree, EmptyTree)))) 

但编译器并不满意这点

type arguments [<notype>,<notype>] do not conform to method apply's type parameter bounds [A,B] 

最终用例用于生成触及的可缓存类型类的实例1k行代码。非参数化版本已经有效，这只是锦上添花。 scalac有一些我不明白的东西，但愿意。你花时间阅读这是非常感谢。

我使用Scala的2.11.8与macro paradise 2.1.0

Answer 1

的问题似乎是，你在的类型参数的地方使用类型参数。这似乎工作（我还必须添加类型参数到defaultApply方法声明）：

val typeArgs = typeParams.map(_.name) 
    val applyDef = q"""${name.toTermName}.apply[..$typeArgs]""" 
    c.warning(c.enclosingPosition, showRaw(applyDef)) 

    q""" 
    object ${name.toTermName} { 
     def defaultApply[..$typeParams]: 
      (..${valueParams.map(_.tpt)}) => $name[..$typeArgs] = $applyDef 
    } 
    """