[英]“error: missing parameter type” during macro splicing
編輯:我發現了我的錯誤-我的遞歸案例的准引用中有一個錯誤,導致它返回格式錯誤的序列
我正在嘗試創建一個將案例類T
轉換為updateMap: Map[String, (play.api.libs.json.JsValue) => Try[(T) => T]]
的宏updateMap: Map[String, (play.api.libs.json.JsValue) => Try[(T) => T]]
( 如何使用scala宏以創建函數對象(以創建Map [String,(T)=> T]) ),其中映射的鍵是case類的字段名稱-這個想法是給定JsObject("key" -> JsValue)
我們可以使用key
從updateMap
檢索適當的更新方法,然后使用JsValue
應用更新。 我在非遞歸情況下進行此工作,即給定一個沒有任何其他案例類作為字段的案例類。 但是,我想擴展此宏,以便它可以為包含其他案例類的案例類生成updateMap
。
case class Inner(innerStr: String)
case class Outer(outerStr: String, inner: Inner)
updateMap[Outer] = {
// updateMap[Inner]
val innerMap = Map("innerStr" -> (str: String) =>
Try { (i: Inner) => i.copy(innerStr = str) } )
// updateMap[Outer]
Map("outerStr" -> (str: String) =>
Try { (o: Outer) => o.copy(outerStr = str) },
"inner.innerStr" -> (str: String) =>
Try { (o: Outer) => innerMap.get("innerStr").get(str).flatMap(lens => o.copy(inner = lens(o.inner))) })}
換句話說,給定updateMap[Outer]
,我將能夠直接更新對象的outerStr
字段,否則,我將能夠更新對象的inner.innerStr
字段,無論哪種方式都返回Try[Outer]
。
該代碼對於非遞歸情況( copyMapRec[Inner]()
)正常工作,但是遞歸情況( copyMapRec[Outer]()
)給我一個“錯誤:缺少參數類型”錯誤-我假設我要么需要在某個地方提供一個隱式參數,否則我對拼接有一個基本的誤解。
下面的代碼使用(String) => Try[(T) => T]
而不是(JsValue) => Try[(T) => T]
因此我不需要將play框架導入到我的REPL。 我使用隱式轉換將JsValue
(或String
)轉換為適當的類型(在val x: $fieldType = str
發生val x: $fieldType = str
行,在基本情況下為准引號;如果沒有適當的隱式轉換,則得到編譯器錯誤)。
import scala.language.experimental.macros
def copyMapImplRec[T: c.WeakTypeTag](c: scala.reflect.macros.Context)(blacklist: c.Expr[String]*): c.Expr[Map[String, (String) => scala.util.Try[(T) => T]]] = {
import c.universe._
// Fields that should be omitted from the map
val blacklistList: Seq[String] = blacklist.map(e => c.eval(c.Expr[String](c.resetAllAttrs(e.tree))))
def rec(tpe: Type): c.Expr[Map[String, (String) => scala.util.Try[(T) => T]]] = {
val typeName = tpe.typeSymbol.name.decoded
// All fields in the case class's primary constructor, minus the blacklisted fields
val fields = tpe.declarations.collectFirst {
case m: MethodSymbol if m.isPrimaryConstructor => m
}.get.paramss.head.filterNot(field => blacklistList.contains(typeName + "." + field.name.decoded))
// Split the fields into case classes and non case classes
val recursive = fields.filter(f => f.typeSignature.typeSymbol.isClass && f.typeSignature.typeSymbol.asClass.isCaseClass)
val nonRecursive = fields.filterNot(f => f.typeSignature.typeSymbol.isClass && f.typeSignature.typeSymbol.asClass.isCaseClass)
val recursiveMethods = recursive.map {
field => {
val fieldName = field.name
val fieldNameDecoded = fieldName.decoded
// Get the c.Expr[Map] for this case class
val map = rec(field.typeSignature)
// Construct an "inner.innerStr -> " seq of tuples from the "innerStr -> " seq of tuples
q"""{
val innerMap = $map
innerMap.toSeq.map(tuple => ($fieldNameDecoded + "." + tuple._1) -> {
(str: String) => {
val innerUpdate = tuple._2(str)
innerUpdate.map(innerUpdate => (outer: $tpe) => outer.copy($fieldName = innerUpdate(outer.$fieldName)))
}
})}"""
}
}
val nonRecursiveMethods = nonRecursive.map {
field => {
val fieldName = field.name
val fieldNameDecoded = fieldName.decoded
val fieldType = field.typeSignature
val fieldTypeName = fieldType.toString
q"""{
$fieldNameDecoded -> {
(str: String) => scala.util.Try {
val x: $fieldType = str
(t: $tpe) => t.copy($fieldName = x)
}.recoverWith {
case e: Exception => scala.util.Failure(new IllegalArgumentException("Failed to parse " + str + " as " + $typeName + "." + $fieldNameDecoded + ": " + $fieldTypeName))
}
}}"""
}
}
// Splice in all of the sequences of tuples, flatten the sequence, and construct a map
c.Expr[Map[String, (String) => scala.util.Try[(T) => T]]] {
q"""{ Map((List(..$recursiveMethods).flatten ++ List(..$nonRecursiveMethods)):_*) }"""
}
}
rec(weakTypeOf[T])
}
def copyMapRec[T](blacklist: String*) = macro copyMapImplRec[T]
我解決了這個問題-最初在我的recursiveMethods
准引用具有innerMap.toSeq(...)
而不是innerMap.toSeq.map(...)
-我忽略了先在REPL中測試代碼
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