scala - Type inference on contents of shapeless HList -

This example is simplified.

I have a set of such classes:

  Case class keymapping [kytype] (k: key type) class wrapped mapping [ketipe] (m: t some { Type T   
 The following types of code are guessed correctly:  < Pre>  val w = new raped mapping (keymapping ("key") // the following statement true error // type mismatch; // found: wktype (with the built-in type string) required: nothing / val test1 : Nothing = wk   
 I have no clue how to guess the right type for the following types:  
  class mappings [ketipe, l & Lt;: HList] (Mapping: L) {val k: KeyType = ???} Val m = New mapping (keymapping ("key 1") :: main mapping ("key 2") :: HNIL) Should not be compiled, the string string should be of test2: nothing = mk   
 what  HList    
  keytype  "Post-T based on the contents of 
 
 Ext "itemprop =" text "> 
 provides a built-in  toList  that is used to convert HLists to lists, is inauspicious.  
 To do this, the first HList should calculate those types of ELUB (at least upper bounds), and something that you can use:  
 < Code> imported useless .ops.hlist.ToList class mapping [l & lt; : HList, Lub] (Mapping: L) (List: ToList [L, Lub]) goes to {...}   
  L , the built-in resolution Drag out of the  L ,  lab  type, which blocks a (and only) valid  toList  example.  
 This is not enough, however, as the  lab  will be the keymap [string] , whereas what you want is  string  is part. To be shapeless in general, the solution is to add another underlying:  
  class mapping [L & lt;: HList, Lub, KeyType] (Mapping: L) (Built-in for list Val: ToList [L, Lib], Val Katie: Lub & Lt ;: & lt; Keymapping [Keytype]] {val k: keytype = null.asInstanceOf [KeyType]}   
 ( There is no need to be implicits  val  s, but if you are looking for things in RPL, then it helps)  
 What is the emphasis that  lob  In this way  KeyMapping [KeyType]   (like it's a subtype or exact same type) , where  KeyType  is still unknown. Then, there is a valid solution for only the specified values, and the  keytype  parameter is drawn as a  string .  
 I do not know how you plan to implement  k , but you think that being a  tolist  example will help you This will help because it gives you the  mappings.toList