斯卡拉案例類轉換

有沒有辦法將一個案件類轉換爲另一種情況下，當他們有相同的領域，並從相同的特質繼承，而不提供轉換器功能（這隻會做一對一的字段映射）？斯卡拉案例類轉換

例如：

trait UberSomething { 
    val name: String 
} 
// these may be located in different files 
case class Something(name: String) extends UberSomething 
case class SomethingOther(name: String) extends UberSomething 

val s = Something("wtv") 
//s.asInstanceOf[SomethingOther] FAILS

來源

2017-04-12 Sofia

無形絕對可以做到這一點，看看http://stackoverflow.com/questions/23192760/safely-copying-fields-between-case-classes-of-different-types –

謝謝，這看起來很有希望 – Sofia

首先從未定義trait成員val如果他們是爲了在以後得以實施點。

trait UberSomething { 
    def name: String 
} 
// these maybe in different files 
case class Something(name: String) extends UberSomething 
case class SomethingOther(name: String) extends UberSomething 

import shapeless._, ops.hlist.Align

另一種方法我在什麼地方＃2見過，所以道歉偷街頭信譽，是使用Align使得字段順序也沒有什麼關係。

class Convert[Target] { 
    def apply[Source, HLS <: HList, HLT <: HList](s: Source)(implicit 

    // Convert the Source to an HList type 
    // include field names, e.g "labelled" 
    // Shapeless "generates" this using an implicit macro 
    // it looks at our type, extracts a list of (Name, Type) pairs 
    genS: LabelledGeneric.Aux[Source, HLS], 

    // Convert the Target o an HList type 
    // include field names, e.g "labelled" 
    // So again we have a (Name, Type) list of pairs this time for Target 
    genT: LabelledGeneric.Aux[Target, HLT], 

    // Use an implicit align to make sure the two HLists 
    // contain the same set of (Name, Type) pairs in arbitrary order. 
    align: Align[HLS, HLT] 
) = genT from align(genS to s) 
} 
// Small trick to guarantee conversion only requires 
// a single type argument, otherwise we'd have to put something 
// in place for HLS and HLT, which are meant to be path dependant 
// and "calculated" by the LabelledGeneric.Repr macro so it wouldn't work as it breaches the "Aux pattern", which exposes a type member materialized by a macro in this case. 
// HLT and HLS come from within genS.Repr and genT.Repr. 
def convert[T] = new Convert[T]

這是一個好一點的HList PARAMS是很好的掩蓋作爲apply一部分，所以你不要自己絆倒了。

val sample = Something("bla") 
convert[SomethingOther](sample) // SomethingOther("bla")

我們來看看這一行：genT from align(genS to s)。

首先genS to s的Source實例轉換爲LabelledGeneric，e.g一個HList與現場信息。
對齊爲Source類型創建的HList的類型和字段以匹配Target類型。
genT from ..允許我們從授予的編譯器可以「證明」的字段和類型爲「所有有」一個HList，這是我們已經有了Align創建Target一個實例。

來源

2017-04-12 14:11:15 flavian

這實際上並沒有在'gen2中編譯爲（gen from obj）' – Sofia

另外，「從來沒有將特徵成員定義爲val，如果它們意味着以後再實施「。 - 你能詳細說明一下，還是指向相關鏈接？謝謝:) – Sofia

@Sofia http://stackoverflow.com/questions/19642053/when-to-use-val-or-def-in-scala-traits。我已經更新了我的答案。 – flavian

你可以做，使用隱式轉換，如：

trait UberSomething { 
    val name: String 
} 

case class Something(name: String) extends UberSomething 
case class SomethingOther(name: String) extends UberSomething 

object Something { 
    implicit def somethingToSomethingOther(s:Something):SomethingOther = SomethingOther(s.name) 
} 
object SomethingOther { 
    implicit def somethingOtherToSomething(s:SomethingOther):Something = Something(s.name) 
} 

val s = Something("wtv") 
val so:SomethingOther = s

來源

2017-04-12 14:00:02 Kris

是的，我知道。創建這些轉換函數（隱式或不）是我試圖避免的。 – Sofia

斯卡拉案例類轉換

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