【发布时间】：2018-10-25 21:41:17
【问题描述】：
我有以下代码，它使用 circe 反序列化一个可以有两种形状的 json（请参阅 jsonPersonalDetails 和 jsonPersonalAddress 的值）。当我尝试从 SearchCriteria 调用方法 transform 时，我得到：
错误：(38, 26) 找不到参数映射器的隐式值：shapeless.ops.coproduct.Mapper.Aux[com.example.circe.CirceShapeApp.transformer.type,com.example.circe.CirceShapeApp.SearchBy ,com.example.circe.CirceShapeApp.JsonPayload]
你能帮我弄清楚为什么隐式映射器没有解析吗？
谢谢！
import io.circe.generic.auto._
import io.circe.shapes._
import io.circe.parser._
import shapeless._
import shapeless.ops.coproduct.Mapper
object CirceShapeApp extends App {
val jsonPersonalDetails = """{"searchCriteria": {"birthDate":"01-01-1980", "lastName":"John"}}""".stripMargin
val jsonPersonalAddress = """{"searchCriteria": {"postalCode":"10776", "houseNumber":"34"}}""".stripMargin
class SearchCriteria(val searchCriteria: SearchBy) {
def transform(implicit mapper: Mapper.Aux[transformer.type, SearchBy, JsonPayload]) = {
searchCriteria map transformer
}
}
case class PersonalDetails(birthDate: String, lastName: String)
case class PersonalAddress(postalCode: String, houseNumber: String)
type SearchBy = PersonalDetails :+: PersonalAddress :+: CNil
type JsonPayload = String :+: CNil
object transformer extends Poly1 {
implicit def casePersonalDetails = at[PersonalDetails](v => s"""{"bd": "${v.birthDate}", "ln":"${v.lastName}"}""")
implicit def casePersonalAddress = at[PersonalAddress](v => s"""{"pc": "${v.postalCode}", "hn":"${v.houseNumber}"}""")
}
val result = decode[SearchCriteria](jsonPersonalDetails).right.get
println(result.searchCriteria.map(transformer)) //WORKS
println(result.transform) //DOESN'T WORK => COMPILATION ERROR
}
【问题讨论】：
-
显然，如果我用 Mapper[transformer.type, SearchBy] 替换 Mapper.Aux[transformer.type, SearchBy, JsonPayload] 代码编译。