programaker · March 7, 2025 12:47 · Oct 21, 2021 · Sep 14, 2021 · Sep 13, 2021
diff --git a/exportClause.scala b/exportClause.scala
@@ -15,20 +15,12 @@ import io.circe.syntax.*
 
 import java.util.UUID
 
-// the pure domain concept
+// the pure domain concept/entity
 // the base data is declared here, and only here
 case class Frunfles(a: String, b: Int, c: Boolean)
 object Frunfles:
   given Encoder[Frunfles] = deriveEncoder
 
-// new entity to be persisted without id
-// no need to make the id optional
-// no need to duplicate Frunfles fields
-case class NewFrunfles(data: Frunfles):
-  export data.* // super-powered delegation!
-object NewFrunfles:
-  given Encoder[NewFrunfles] = Encoder.instance(_.data.asJson)
-
 // persisted entity containing an id
 // no need to make the id optional
 // no need to duplicate Frunfles fields
@@ -40,20 +32,15 @@ object PersistedFrunfles:
 
 // type-safe operations
 // explictly stating which operations require an entity with id
-def insert(f: NewFrunfles): PersistedFrunfles = ???
+def insert(f: Frunfles): PersistedFrunfles = ???
 def update(f: PersistedFrunfles): PersistedFrunfles = ???
 def delete(f: PersistedFrunfles): Unit = ???
 
 // composition over inheritance, more FP-ish
 val f = Frunfles("Meh", 42, true)
-val nf = NewFrunfles(data = f)
 val pf = PersistedFrunfles(id = UUID.randomUUID().nn, data = f)
 
-// exported fields available without calling `.data`
-val a1 = nf.a
-val b1 = nf.b
-val c1 = nf.c
-///
+// exported fields available without calling `.data`. Happy demeter!
 val id = pf.id
 val a2 = pf.a
 val b2 = pf.b

diff --git a/exportClause.scala b/exportClause.scala
@@ -1,6 +1,6 @@
 /*
 * The good practices say we shouldn't use the same type for everything (domain, json, persistence, ...), but
-* most of the time those types are very similar - if not exactly identical - creating a lot of dupliation.
+* most of the time those types are very similar - if not exactly identical - creating a lot of duplication.
 *
 * Inheritance to the rescue? Nah... not very FP and even the OOP folks are aware that we should
 * prefer composition over it. But composition has it's own challenges (Law of Demeter for instance).

diff --git a/exportClause.scala b/exportClause.scala
@@ -0,0 +1,60 @@
+/*
+* The good practices say we shouldn't use the same type for everything (domain, json, persistence, ...), but
+* most of the time those types are very similar - if not exactly identical - creating a lot of dupliation.
+*
+* Inheritance to the rescue? Nah... not very FP and even the OOP folks are aware that we should
+* prefer composition over it. But composition has it's own challenges (Law of Demeter for instance).
+*
+* Let's see how the new `Export Clauses` in Scala 3 can help with that:
+* https://docs.scala-lang.org/scala3/reference/other-new-features/export.html
+* */
+
+import io.circe.Encoder
+import io.circe.generic.semiauto.*
+import io.circe.syntax.*
+
+import java.util.UUID
+
+// the pure domain concept
+// the base data is declared here, and only here
+case class Frunfles(a: String, b: Int, c: Boolean)
+object Frunfles:
+  given Encoder[Frunfles] = deriveEncoder
+
+// new entity to be persisted without id
+// no need to make the id optional
+// no need to duplicate Frunfles fields
+case class NewFrunfles(data: Frunfles):
+  export data.* // super-powered delegation!
+object NewFrunfles:
+  given Encoder[NewFrunfles] = Encoder.instance(_.data.asJson)
+
+// persisted entity containing an id
+// no need to make the id optional
+// no need to duplicate Frunfles fields
+case class PersistedFrunfles(id: UUID, data: Frunfles):
+  export data.*
+object PersistedFrunfles:
+  // easy to avoid exposing the id in Json
+  given Encoder[PersistedFrunfles] = Encoder.instance(_.data.asJson)
+
+// type-safe operations
+// explictly stating which operations require an entity with id
+def insert(f: NewFrunfles): PersistedFrunfles = ???
+def update(f: PersistedFrunfles): PersistedFrunfles = ???
+def delete(f: PersistedFrunfles): Unit = ???
+
+// composition over inheritance, more FP-ish
+val f = Frunfles("Meh", 42, true)
+val nf = NewFrunfles(data = f)
+val pf = PersistedFrunfles(id = UUID.randomUUID().nn, data = f)
+
+// exported fields available without calling `.data`
+val a1 = nf.a
+val b1 = nf.b
+val c1 = nf.c
+///
+val id = pf.id
+val a2 = pf.a
+val b2 = pf.b
+val c2 = pf.c