我想知道是否有人可以就我遇到的问题提供一些见解。我已经用一些代码和解释我的问题做了主旨:https://gist.github.com/tbrown1979/9993f07c8f4fa2786c83
基本上我试图制作一些允许我将List [String]转换为case类的东西。我已经制作了一个允许我这样做的阅读器,但是我遇到了一个问题,即为案例类定义的Reader不能包含一个单独的案例类的阅读器。
查看'非工作示例'下面 - 我遇到一个问题,在阅读时,我不知道要从列表中提取多少项。对于持有测试的Bar,我需要拉出2个元素(因为Test有两个参数)。有没有办法让我知道案例类只有其类型的字段数量?有一个更好的方法吗?
以下是如何使用Reader的示例。我也包括了一个非工作的例子。
////Working Example////
case class Foo(a: Int, s: String)
object Foo {
implicit val FooReader : Reader[Foo] =
Reader[Int :: String :: HNil].map(Generic[Foo].from _)
}
val read: ValidationNel[String, Foo] = Reader.read[Foo](List("12","text"))
println(read)//Success(Foo(12, "text"))
///////////////////////////
////Non-working Example////
case class Test(a: Int, b: String)
object Test {
implicit val TestReader: Reader[Test] =
Reader[Int :: String :: HNil].map(Generic[Test].from _)
}
case class Bar(c: Test)
object Bar {
implicit val BarReader: Reader[Bar] =
Reader[Test :: HNil].map(Generic[Bar].from _)
}
val barRead = Reader.read[Bar](List("21", "someString"))
println(barRead) //Failure(NonEmptyList("Invalid String: List()", "Exepected empty, but contained value"))
//////////////////////////
答案 0 :(得分:0)
这样的事情对我有用(修改this)
object ShapelessStringToTypeConverters {
import cats._, implicits._, data.ValidatedNel
import mouse._, string._, option._
import shapeless._, labelled._
private type Result[A] = ValidatedNel[ParseFailure, A]
case class ParseFailure(error: String)
trait Convert[V] {
def parse(input: String): Result[V]
}
object Convert {
def to[V](input: String)(implicit C: Convert[V]): Result[V] =
C.parse(input)
def instance[V](body: String => Result[V]): Convert[V] = new Convert[V] {
def parse(input: String): Result[V] = body(input)
}
implicit def booleans: Convert[Boolean] =
Convert.instance(
s =>
s.parseBooleanValidated
.leftMap(e => ParseFailure(s"Not a Boolean ${e.getMessage}"))
.toValidatedNel)
implicit def ints: Convert[Int] =
Convert.instance(
s =>
s.parseIntValidated
.leftMap(e => ParseFailure(s"Not an Int ${e.getMessage}"))
.toValidatedNel)
implicit def longs: Convert[Long] =
Convert.instance(
s =>
s.parseLongValidated
.leftMap(e => ParseFailure(s"Not an Long ${e.getMessage}"))
.toValidatedNel)
implicit def doubles: Convert[Double] =
Convert.instance(
s =>
s.parseDoubleValidated
.leftMap(e => ParseFailure(s"Not an Double ${e.getMessage}"))
.toValidatedNel)
implicit def strings: Convert[String] = Convert.instance(s => s.validNel)
}
//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
sealed trait SchemaMap[A] {
def readFrom(input: Map[String, String]): ValidatedNel[ParseFailure, A]
}
object SchemaMap {
def of[A](implicit s: SchemaMap[A]): SchemaMap[A] = s
private def instance[A](body: Map[String, String] => Result[A]): SchemaMap[A] = new SchemaMap[A] {
def readFrom(input: Map[String, String]): Result[A] =
body(input)
}
implicit val noOp: SchemaMap[HNil] =
SchemaMap.instance(_ => HNil.validNel)
implicit def parsing[K <: Symbol, V: Convert, T <: HList](implicit key: Witness.Aux[K], next: SchemaMap[T]): SchemaMap[FieldType[K, V] :: T] =
SchemaMap.instance { input =>
val fieldName = key.value.name
val parsedField = input
.get(fieldName)
.cata(entry => Convert.to[V](entry), ParseFailure(s"$fieldName is missing").invalidNel)
.map(f => field[K](f))
(parsedField, next.readFrom(input)).mapN(_ :: _)
}
implicit def classes[A, R <: HList](implicit repr: LabelledGeneric.Aux[A, R], schema: SchemaMap[R]): SchemaMap[A] =
SchemaMap.instance { input =>
schema.readFrom(input).map(x => repr.from(x))
}
}
//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
sealed trait SchemaList[A] {
def readFrom(input: List[String]): ValidatedNel[ParseFailure, A]
}
object SchemaList {
def of[A](implicit s: SchemaList[A]): SchemaList[A] = s
private def instance[A](body: List[String] => Result[A]): SchemaList[A] = new SchemaList[A] {
def readFrom(input: List[String]): Result[A] = body(input)
}
implicit val noOp: SchemaList[HNil] =
SchemaList.instance(_ => HNil.validNel)
implicit def parsing[K <: Symbol, V: Convert, T <: HList](implicit key: Witness.Aux[K], next: SchemaList[T]): SchemaList[FieldType[K, V] :: T] =
SchemaList.instance { input =>
val fieldName = key.value.name
val parsedField = input
.headOption
.cata(entry => Convert.to[V](entry), ParseFailure(s"$fieldName is missing").invalidNel)
.map(f => field[K](f))
(parsedField, next.readFrom(input.tail)).mapN(_ :: _)
}
implicit def classes[A, R <: HList](implicit repr: LabelledGeneric.Aux[A, R], schema: SchemaList[R]): SchemaList[A] =
SchemaList.instance { input =>
schema.readFrom(input).map(x => repr.from(x))
}
}
}
/*
case class Foo(a: String, b: Int, c: Boolean)
def m: Map[String, String] = Map("a" -> "hello", "c" -> "true", "b" -> "100")
def e: Map[String, String] = Map("c" -> "true", "b" -> "a100")
val result = SchemaMap.of[Foo].readFrom(m)
val lst = List("145164983", "0.01862523", "16.11681596", "21:38:57", "bid")
case class Trade0(tid: Long, price: Double, amount: Double, time: String, tpe: String)
val result2 = SchemaList.of[Trade0].readFrom(lst)
*/