Establish bounds for type members within a type alias in Scala -

given:

trait record {   type id   val id: id }  trait datasource {   type id   def read(id: id): try[r] } 

i'd able describe read function generically.

type reader[r <: record, ds <: datasource] = (ds#id) => try[r] 

how can guarantee type safety here such ds#id won't dissimilar type r#id? tried...

type reader[r <: record, ds <: datasource, r#id <: ds#id] = (ds#id) => try[r] 

but doens't compile. correct syntax situation?

when dealing type parameters of reader, id has pulled out it's own parameter.

type reader[r <: record, ds <: datasource, id] = (id) => try[r] 

once done it's possible place additional bounds onto it...

type reader[r <: record, ds <: datasource, id <: ds#id =:= r#id] = (id) => try[r]