在我的macro impl中有这样一个例子：

def renderJsonFn(rt: RType): Expr[(Any,StringBuilder) => StringBuilder] = 

  val reflectedClassFieldInfo = ???
  val typeMaker = reflectedClassFieldInfo.fieldType.toType // (quotes: Quotes) => TypeRepr
  val fieldType = typeMaker(quotes).asType // Type[? <: AnyKind]

  '{(a:Any, sb:StringBuilder) => 

     val typedA = ?? // <<— need equivalent of a.asInstanceOf[fieldType] here

     val typedFieldValue = ${ 
       Select.unique('{ typedA }.asTerm, someFieldName).asExpr 
     }
     // This fails if I use ‘a’ —> someFieldName is not a member of Any
     // Having a:T is highly impractical—and just moves the problem.  Still need a way to typecast in a macro 
  }