我正在尝试Shapeless
从quasiquote
with中调用宏Scala
,但没有得到我想要的东西。
我的宏不会返回任何错误,但不会扩展Witness(fieldName)
为Witness.Lt[String]
val implicits = schema.fields.map { field =>
val fieldName:String = field.name
val fieldType = TypeName(field.valueType.fullName)
val in = TermName("implicitField"+fieldName)
val tn = TermName(fieldName)
val cc = TermName("cc")
q"""implicit val $in = Field.apply[$className,$fieldType](Witness($fieldName), ($cc: $className) => $cc.$tn)"""
}
这是我的Field
定义:
sealed abstract class Field[CC, FieldName] {
val fieldName: String
type fieldType
// How to extract this field
def get(cc : CC) : fieldType
}
object Field {
// fieldType is existencial in Field but parametric in Fied.Aux
// used to explict constraints on fieldType
type Aux[CC, FieldName, fieldType_] = Field[CC, FieldName] {
type fieldType = fieldType_
}
def apply[CC, fieldType_](fieldWitness : Witness.Lt[String], ext : CC => fieldType_) : Field.Aux[CC, fieldWitness.T, fieldType_] =
new Field[CC, fieldWitness.T] {
val fieldName : String = fieldWitness.value
type fieldType = fieldType_
def get(cc : CC) : fieldType = ext(cc)
}
}
在这种情况下,我生成的隐式如下所示:
implicit val implicitFieldname : Field[MyCaseClass, fieldWitness.`type`#T]{
override type fieldType = java.lang.String
}
如果已在外部定义quasiquote
,则会生成如下内容:
implicit val implicitFieldname : Field.Aux[MyCaseClass, Witness.Lt[String]#T, String] = ...
有什么可以做的吗?
@TravisBrown是的,我正在使用宏注释(Macro Paradise)来构建它。我试图提供这样的类型:
—
Roch
q"""implicit val $in : Field.Aux[$className, Witness.Lt[String]#T, String] = Field.apply[$className,$fieldType](Witness($fieldName), ($cc: $className) => $cc.$tn)"""
$in
(我认为需要使用ConstantType
)?