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November 23, 2021 13:25
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Doobie instances for NewType
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| import io.estatico.newtype.ops._ | |
| import io.estatico.newtype.macros.newtype | |
| import eu.timepit.refined.api.Refined | |
| import doobie.implicits._ | |
| import doobie.postgres.implicits._ | |
| import doobie.refined.implicits._ | |
| /** | |
| * Derive a Put (so it can be interpolated in doobie sql expressions) for any newtype backed by a type that is | |
| * supported by doobie (e.g. any wrapper of String, UUID, Boolean etc) | |
| * | |
| * if a: A has a Coercible[A, B] means one can transform a to b: B via a.coerce[B] | |
| */ | |
| implicit def newTypePut[N: Coercible[*, R], R: Put]: Put[N] = Put[R].contramap[N](_.coerce[R]) | |
| implicit def newTypeRead[N: Coercible[R, *], R: Read]: Read[N] = Read[R].map(_.asInstanceOf[N]) | |
| /** If we have an Eq instance for Repr type R, derive an Eq instance for NewType N. */ | |
| implicit def coercibleEq[R, N](implicit ev: Coercible[Eq[R], Eq[N]], R: Eq[R]): Eq[N] = | |
| ev(R) | |
| /* | |
| * With this one can create value classes like these and embed them in doobie fragments | |
| */ | |
| @newtype case class UserId(value: UUID) | |
| val userId: UserId = ??? | |
| val fragment = sql"select * from users where user_id = $userId" |
with newtype 0.4.4, I got
value repr is not a member of type parameter N
implicit def newTypePut[N: Coercible[R, *], R: Put]: Put[N] = Put[R].contramap[N](_.repr.asInstanceOf[R])
This compiled:
implicit def newTypePut[B, A](implicit ev: Coercible[B, A], evp: Put[A]): Put[B] = evp.contramap[B](ev(_))
Thanks, I fixed it for 0.4.4
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Why newTypePut/newTypeRead doesn't the same as coercibleEq? ie if we have Read[R], and Coercible[Read[N], Read[R]] we can get Read[N]? Also the solution doesn't work with latest version of newtype