Scala 2.13
我有很多类似的特征
trait SomeTrait[F[_]]{
def someOp(): F[Unit]
//...
}
及其实现
class SomeTraitImpl[F[_]: Sync] extends SomeTrait[F]{
//...
}
object SomeTrait{
def apply[F[_]: Sync](): SomeTrait[F] = new SomeTraitImpl[F]()
}
问题是,与这种apply方法一起使用的情况看起来很难看,这是一个样板。有没有一种方法可以自动生成object
? Simulacrum或其他任何东西(手写的宏注释吗?)可以做到吗?
您可以使用macro annotation
import scala.annotation.{StaticAnnotation, compileTimeOnly}
import scala.language.experimental.macros
import scala.reflect.macros.blackbox
@compileTimeOnly("enable macro paradise")
class implApply extends StaticAnnotation {
def macroTransform(annottees: Any*): Any = macro ImplApplyMacro.macroTransformImpl
}
object ImplApplyMacro {
def macroTransformImpl(c: blackbox.Context)(annottees: c.Tree*): c.Tree = {
import c.universe._
annottees match {
case q"$mods trait $tpname[..$tparams] extends { ..$earlydefns } with ..$parents { $self => ..$stats }" ::
q"$mods1 object $tname extends { ..$earlydefns1 } with ..$parents1 { $self1 => ..$body }" :: Nil =>
val tparams1 = tparams.map {
case q"$mods type $tpname[..$tparams] = $tpt" => tq"$tpname"
}
q"""
$mods trait $tpname[..$tparams] extends { ..$earlydefns } with ..$parents { $self => ..$stats }
$mods1 object $tname extends { ..$earlydefns1 } with ..$parents1 { $self1 =>
def apply[..$tparams]()(implicit sync: Sync[${tparams1.head}]): $tpname[..$tparams1] = new ${TypeName(tpname + "Impl")}[..$tparams1]()
..$body
}
"""
}
}
}
@implApply
trait SomeTrait[F[_]]{
def someOp(): F[Unit]
}
class SomeTraitImpl[F[_]: Sync] extends SomeTrait[F]{
override def someOp(): F[Unit] = ???
}
object SomeTrait
//Warning:scalac: {
// object SomeTrait extends scala.AnyRef {
// def <init>() = {
// super.<init>();
// ()
// };
// def apply[F[_]]()(implicit sync: Sync[F]): SomeTrait[F] = new SomeTraitImpl[F]()
// };
// ()
//}
此注释期望伴随对象存在,并向其中添加apply
。如果伴侣对象不存在,那么在这种情况下应创建它,然后应对此宏注释进行一些修改: