斯卡拉宏註釋 - 具有類型參數的案例類

Question

我想爲向伴隨對象添加方法的案例類編寫一個簡單的宏註釋。問題在於新方法必須考慮帶註釋的案例類的類型參數。

下面是我需要傳遞

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)) 
    } 
} 

這裏是我寫我的理解是，當我嘗試lift的做到這一點

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") 
    } 
    } 
} 

該問題的代碼測試類型參數列表到結果語法樹中，它們不會被識別爲與原始樹相同的類型參數。

那麼我專注於是，宏觀

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

這部分原料語法樹的發射是由於

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)))) 

但編譯器並不滿意這點

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

最終用例用於生成觸及的可緩存類型類的實例1k行代碼。非參數化版本已經有效，這只是錦上添花。 scalac有一些我不明白的東西，但願意。你花時間閱讀這是非常感謝。

我使用Scala的2.11.8與macro paradise 2.1.0

Answer 1

的問題似乎是，你在的類型參數的地方使用類型參數。這似乎工作（我還必須添加類型參數到defaultApply方法聲明）：

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 
    } 
    """