Created
December 7, 2012 16:29
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Simple macro-based wrapper example
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import scala.language.experimental.macros | |
import scala.reflect.macros.Context | |
object WrapperExample { | |
def wrap[A](a: A): A = macro wrap_impl[A] | |
def wrap_impl[A: c.WeakTypeTag](c: Context)(a: c.Expr[A]) = { | |
import c.universe._ | |
val wrapped = weakTypeOf[A] | |
val f = Select(reify(Predef).tree, "println") | |
val methods = wrapped.declarations.collect { | |
case m: MethodSymbol if !m.isConstructor => DefDef( | |
Modifiers(Flag.OVERRIDE), | |
m.name, | |
Nil, Nil, | |
TypeTree(), | |
Block( | |
Apply(f, c.literal("Calling: " + m.name.decoded).tree :: Nil), | |
Select(a.tree, m.name) | |
) | |
) | |
}.toList | |
val constructor = DefDef( | |
Modifiers(), nme.CONSTRUCTOR, Nil, Nil :: Nil, TypeTree(), | |
Block( | |
Apply( | |
Select(Super(This(tpnme.EMPTY), tpnme.EMPTY), nme.CONSTRUCTOR), Nil | |
) :: Nil, | |
c.literalUnit.tree | |
) | |
) | |
val anon = c.fresh | |
c.Expr(Block( | |
ClassDef(Modifiers(Flag.FINAL), newTypeName(anon), Nil, | |
Template( | |
List(Ident(wrapped.typeSymbol.name)), | |
emptyValDef, | |
constructor :: methods | |
) | |
) :: Nil, | |
Apply(Select(New(Ident(newTypeName(anon))), nme.CONSTRUCTOR), Nil) | |
)) | |
} | |
} |
A discussion of a subtle error in this code: http://groups.google.com/group/scala-internals/browse_thread/thread/492560d941b315cc
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See http://stackoverflow.com/questions/13767582/creating-a-method-definition-tree-from-a-method-symbol-and-a-body for an explanation and related dicsussion.