Change fields of case class based on map entries with simple type check in scala macros

Change fields of case class based on map entries with simple type check in
scala macros

I want to write a scala macros that can override field values of case
class based on map entries with simple type check. In case original field
type and override value type are compatible set new value otherwise keep
original value.
So far I have following code:
import language.experimental.macros
import scala.reflect.macros.Context
object ProductUtils {
def withOverrides[T](entity: T, overrides: Map[String, Any]): T =
macro withOverridesImpl[T]
def withOverridesImpl[T: c.WeakTypeTag](c: Context)
(entity: c.Expr[T],
overrides:
c.Expr[Map[String, Any]]):
c.Expr[T] = {
import c.universe._
val originalEntityTree = reify(entity.splice).tree
val originalEntityCopy =
entity.actualType.member(newTermName("copy"))
val originalEntity =
weakTypeOf[T].declarations.collect {
case m: MethodSymbol if m.isCaseAccessor =>
(m.name, c.Expr[T](Select(originalEntityTree,
m.name)), m.returnType)
}
val values =
originalEntity.map {
case (name, value, ctype) =>
AssignOrNamedArg(
Ident(name),
{
def reifyWithType[K: WeakTypeTag] = reify {
overrides
.splice
.asInstanceOf[Map[String, Any]]
.get(c.literal(name.decoded).splice)
match {
case Some(newValue : K) =>
newValue
case _ =>
value.splice
}
}
reifyWithType(c.WeakTypeTag(ctype)).tree
}
)
}.toList
originalEntityCopy match {
case s: MethodSymbol =>
c.Expr[T](
Apply(Select(originalEntityTree,
originalEntityCopy), values))
case _ => c.abort(c.enclosingPosition, "No eligible copy
method!")
}
}
}
Executed like this:
import macros.ProductUtils
case class Example(field1: String, field2: Int, filed3: String)
object MacrosTest {
def main(args: Array[String]) {
val overrides = Map("field1" -> "new value", "field2" ->
"wrong type")
println(ProductUtils.withOverrides(Example("", 0, ""),
overrides)) // Example("new value", 0, "")
}
}
As you can see, I've managed to get type of original field and now want to
pattern match on it in reifyWithType.
Unfortunately in current implementation I`m getting a warning during
compilation:
warning: abstract type pattern K is unchecked since it is eliminated by
erasure case Some(newValue : K) => newValue
and a compiler crash in IntelliJ:
Exception in thread "main" java.lang.NullPointerException
at
scala.tools.nsc.transform.Erasure$ErasureTransformer$$anon$1.preEraseAsInstanceOf$1(Erasure.scala:1032)
at
scala.tools.nsc.transform.Erasure$ErasureTransformer$$anon$1.preEraseNormalApply(Erasure.scala:1083)
at
scala.tools.nsc.transform.Erasure$ErasureTransformer$$anon$1.preEraseApply(Erasure.scala:1187)
at
scala.tools.nsc.transform.Erasure$ErasureTransformer$$anon$1.preErase(Erasure.scala:1193)
at
scala.tools.nsc.transform.Erasure$ErasureTransformer$$anon$1.transform(Erasure.scala:1268)
at
scala.tools.nsc.transform.Erasure$ErasureTransformer$$anon$1.transform(Erasure.scala:1018)
at scala.reflect.internal.Trees$class.itransform(Trees.scala:1217)
at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:13)
at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:13)
at scala.reflect.api.Trees$Transformer.transform(Trees.scala:2897)
at
scala.tools.nsc.transform.TypingTransformers$TypingTransformer.transform(TypingTransformers.scala:48)
at
scala.tools.nsc.transform.Erasure$ErasureTransformer$$anon$1.transform(Erasure.scala:1280)
at
scala.tools.nsc.transform.Erasure$ErasureTransformer$$anon$1.transform(Erasure.scala:1018)
So the questions are:
* Is it possible to make type comparison of type received in macro to
value runtime type?
* Or is there any better approach to solve this task?