extendAbstract

src/TraitBuilder.ts

@@ -57,6 +57,19 @@ export class TraitBuilder<
         )
     }
 
+    extendAbstract<
+        A extends Abstract
+    >(
+        abstract: (Super: AbstractClass<Abstract>) => AbstractClass<A, []>
+    ) {
+        return new TraitBuilder(
+            this.traitSuperExpression,
+            {} as A,
+            this.traitStaticAbstract,
+            this.traitApply,
+        )
+    }
+
     implement<
         ImplClassWithAbstract extends (
             Class<Abstract, []> &

src/tests.ts

@@ -28,14 +28,22 @@ const Identifiable = <ID>() => trait
     .build()
 
 const StatefulSubscription = trait
-    .abstract<{
-        readonly isStatefulSubscription: true
-        readonly status: (
+    // .abstract<{
+    //     readonly isStatefulSubscription: true
+    //     readonly status: (
+    //         { _tag: "awaitingPayment" } |
+    //         { _tag: "active", activeSince: Date, expiresAt?: Date } |
+    //         { _tag: "expired", expiredSince: Date }
+    //     )
+    // }>()
+    .extendAbstract(Super => class extends Super {
+        readonly isStatefulSubscription!: true
+        readonly status!: (
             { _tag: "awaitingPayment" } |
             { _tag: "active", activeSince: Date, expiresAt?: Date } |
             { _tag: "expired", expiredSince: Date }
         )
-    }>()
+    })
     .build()
 
 type StatefulSubscriptionClass = Trait.Class<typeof StatefulSubscription>