src/Trait.ts

@@ -4,7 +4,7 @@ import { AbstractTag, TraitExpression, emptyTraitExpression } from "."
 import { StaticMembers } from "./util"
 
 
-type AddAbstractToImplClass<
+export type AddAbstractToImplClass<
     ImplClass extends Class<{}, []>,
     Abstract  extends {},
 > = (
@@ -15,7 +15,7 @@ type AddAbstractToImplClass<
     StaticMembers<ImplClass>
 )
 
-type RemoveAbstractFromImplClass<
+export type RemoveAbstractFromImplClass<
     ImplClassWithAbstract extends Class<Abstract, []>,
     Abstract              extends {},
 > = (

src/TraitExpression.ts

@@ -1,7 +1,7 @@
 import { Call, Fn, Pipe, Tuples } from "hotscript"
-import { AbstractClass, Class, Opaque } from "type-fest"
-import { AbstractTag, Trait, TraitApplierSuperTag } from "."
-import { ExtendFn, SimplifyFn, StaticMembersFn } from "./util"
+import { AbstractClass, Class, Opaque, Simplify } from "type-fest"
+import { AbstractTag, RemoveAbstractFromImplClass, Trait, TraitApplierSuperTag } from "."
+import { CommonKeys, ExtendFn, KeysOnlyInLeft, SimplifyFn, StaticMembersFn } from "./util"
 
 
 export class TraitExpression<
@@ -44,18 +44,22 @@ export class TraitExpression<
     }
 
     subtrait<
-        SubtraitAbstract         extends {},
-        SubtraitImplWithAbstract extends Class<{}>,
+        SubtraitAbstract              extends Implements<typeof this>,
+        SubtraitImplClassWithAbstract extends Class<SubtraitAbstract, []>,
     >(
-        abstract: (
-            abstract: Pipe<typeof this, [
-
-            ]>
-        ) => Opaque<SubtraitAbstract, AbstractTag>,
-
-        // impl: ()
+        abstract: (expression: typeof this) => Opaque<SubtraitAbstract, AbstractTag>,
+        apply: (Super: Opaque<AbstractClass<SubtraitAbstract>, TraitApplierSuperTag>) => (
+            Opaque<SubtraitImplClassWithAbstract, TraitApplierSuperTag>
+        ),
     ) {
-
+        return new Trait(
+            this,
+            {} as Simplify<
+                CommonKeys<SubtraitAbstract, Implements<typeof this>> &
+                KeysOnlyInLeft<SubtraitAbstract, Implements<typeof this>>
+            >,
+            apply as any as (Super: AbstractClass<{}>) => RemoveAbstractFromImplClass<SubtraitImplClassWithAbstract, SubtraitAbstract>,
+        )
     }
 }
 
@@ -90,6 +94,12 @@ export namespace TraitExpression {
     }
 }
 
+export const emptyTraitExpression = new TraitExpression(
+    TraitExpression.NullSuperclass,
+    [] as const,
+    [] as const,
+)
+
 
 export type Implements<Exp extends TraitExpression<any, any, any>> = (
     Exp extends TraitExpression<any, infer AllTraits, any>
@@ -100,10 +110,3 @@ export type Implements<Exp extends TraitExpression<any, any, any>> = (
         ]>
         : never
 )
-
-
-export const emptyTraitExpression = new TraitExpression(
-    TraitExpression.NullSuperclass,
-    [] as const,
-    [] as const,
-)

src/TraitExpressionBuilder.ts

@@ -4,6 +4,67 @@ import { Trait, TraitExpression, emptyTraitExpression } from "."
 import { ExtendableFn, StaticMembersFn } from "./util"
 
 
+type SpreadSupertraits<Traits extends Trait<any, any, any>[]> = (
+    Call<
+        Tuples.FlatMap<PrependTraitSupertraitsFn>,
+        Traits
+    >
+)
+interface PrependTraitSupertraitsFn extends Fn {
+    return: [...Trait.Supertraits<this["arg0"]>, this["arg0"]]
+}
+
+
+type AbstractMembersExtendable<
+    Superclass extends AbstractClass<{}>,
+    Traits     extends Trait<any, any, any>[],
+> = (
+    Call<ExtendableFn, [
+        InstanceType<Superclass>,
+        ...Call<Tuples.Map<Trait.OwnAbstractFn>, Traits>,
+    ]>
+)
+
+type ImplInstanceExtendable<
+    Superclass extends AbstractClass<{}>,
+    Traits     extends Trait<any, any, any>[],
+> = (
+    Call<ExtendableFn, [
+        InstanceType<Superclass>,
+        ...Call<Tuples.Map<Trait.OwnImplInstanceFn>, Traits>,
+    ]>
+)
+
+type ImplStaticMembersExtendable<
+    Superclass extends AbstractClass<{}>,
+    Traits     extends Trait<any, any, any>[],
+> = (
+    Pipe<[
+        Superclass,
+        ...Call<Tuples.Map<Trait.OwnImplClassFn>, Traits>,
+    ], [
+        Tuples.Map<StaticMembersFn>,
+        ExtendableFn,
+    ]>
+)
+
+type BuildTraitExpression<
+    Superclass extends AbstractClass<{}>,
+    OwnTraits  extends Trait<any, any, any>[],
+    AllTraits  extends Trait<any, any, any>[],
+> = (
+    Call<Tuples.IsEmpty, AllTraits> extends true
+        ? "Cannot express an empty list of traits."
+        : AbstractMembersExtendable<Superclass, AllTraits> extends false
+            ? "Type conflict between the traits abstract members and/or the superclass instance."
+            : ImplInstanceExtendable<Superclass, AllTraits> extends false
+                ? "Type conflict between the traits implementation instances and/or the superclass instance."
+                : ImplStaticMembersExtendable<Superclass, AllTraits> extends false
+                    ? "Type conflict between the traits implementation static members and/or the superclass static members."
+                    : TraitExpression<Superclass, OwnTraits, AllTraits>
+)
+
+
 class TraitExpressionBuilder<
     Super     extends AbstractClass<{}>,
     OwnTraits extends Trait<any, any, any>[],
@@ -67,66 +128,4 @@ class TraitExpressionBuilder<
     }
 }
 
-
-type SpreadSupertraits<Traits extends Trait<any, any, any>[]> = (
-    Call<
-        Tuples.FlatMap<PrependTraitSupertraitsFn>,
-        Traits
-    >
-)
-interface PrependTraitSupertraitsFn extends Fn {
-    return: [...Trait.Supertraits<this["arg0"]>, this["arg0"]]
-}
-
-
-type AbstractMembersExtendable<
-    Superclass extends AbstractClass<{}>,
-    Traits     extends Trait<any, any, any>[],
-> = (
-    Call<ExtendableFn, [
-        InstanceType<Superclass>,
-        ...Call<Tuples.Map<Trait.OwnAbstractFn>, Traits>,
-    ]>
-)
-
-type ImplInstanceExtendable<
-    Superclass extends AbstractClass<{}>,
-    Traits     extends Trait<any, any, any>[],
-> = (
-    Call<ExtendableFn, [
-        InstanceType<Superclass>,
-        ...Call<Tuples.Map<Trait.OwnImplInstanceFn>, Traits>,
-    ]>
-)
-
-type ImplStaticMembersExtendable<
-    Superclass extends AbstractClass<{}>,
-    Traits     extends Trait<any, any, any>[],
-> = (
-    Pipe<[
-        Superclass,
-        ...Call<Tuples.Map<Trait.OwnImplClassFn>, Traits>,
-    ], [
-        Tuples.Map<StaticMembersFn>,
-        ExtendableFn,
-    ]>
-)
-
-type BuildTraitExpression<
-    Superclass extends AbstractClass<{}>,
-    OwnTraits  extends Trait<any, any, any>[],
-    AllTraits  extends Trait<any, any, any>[],
-> = (
-    Call<Tuples.IsEmpty, AllTraits> extends true
-        ? "Cannot express an empty list of traits."
-        : AbstractMembersExtendable<Superclass, AllTraits> extends false
-            ? "Type conflict between the traits abstract members and/or the superclass instance."
-            : ImplInstanceExtendable<Superclass, AllTraits> extends false
-                ? "Type conflict between the traits implementation instances and/or the superclass instance."
-                : ImplStaticMembersExtendable<Superclass, AllTraits> extends false
-                    ? "Type conflict between the traits implementation static members and/or the superclass static members."
-                    : TraitExpression<Superclass, OwnTraits, AllTraits>
-)
-
-
 export const expression = new TraitExpressionBuilder(emptyTraitExpression)

src/tests.ts

@@ -1,4 +1,4 @@
-import { Implements, abstract, expression, trait } from "."
+import { Implements, Trait, abstract, expression, trait } from "."
 
 
 const PrintsHelloOnNew = trait(
@@ -22,6 +22,7 @@ const Identifiable = <ID>() => trait(
 
 const StatefulSubscription = trait(
     abstract<{
+        readonly isStatefulSubscription: true
         readonly status: (
             { _tag: "awaitingPayment" } |
             { _tag: "active", activeSince: Date, expiresAt?: Date } |
@@ -32,14 +33,23 @@ const StatefulSubscription = trait(
     Super => class StatefulSubscription extends Super {},
 )
 
-// interface ActiveStatefulSubscriptionAbstractMembers extends TraitAbstractMembers<typeof StatefulSubscription> {
-//     readonly status: { _tag: "active", activeSince: Date, expiresAt?: Date }
-// }
+const ActiveStatefulSubscription = expression
+    .expresses(StatefulSubscription)
+    .build()
+    .subtrait(
+        exp => {
+            interface IActiveStatefulSubscription extends Implements<typeof exp> {
+                readonly isActiveStatefulSubscription: true
+                readonly status: { _tag: "active", activeSince: Date, expiresAt?: Date }
+            }
 
-// const ActiveStatefulSubscription = trait(
-//     abstract<ActiveStatefulSubscriptionAbstractMembers>(),
-//     Super => class ActiveStatefulSubscription extends Super {},
-// )
+            return abstract<IActiveStatefulSubscription>()
+        },
+
+        Super => class ActiveStatefulSubscription extends Super {},
+    )
+
+type T = Trait.OwnAbstract<typeof ActiveStatefulSubscription>
 
 
 class TestSuperclass {
@@ -47,7 +57,6 @@ class TestSuperclass {
     // static test = 69
 }
 
-
 const exp = expression
     .extends(TestSuperclass)
     .expresses(
@@ -71,6 +80,7 @@ type Abs = Implements<typeof exp>
 // )
 
 class User extends exp.extends implements Implements<typeof exp> {
+    readonly isStatefulSubscription: true = true
     declare status: { _tag: "awaitingPayment" } | { _tag: "active"; activeSince: Date; expiresAt?: Date | undefined } | { _tag: "expired"; expiredSince: Date }
     id: bigint = -1n
 }

src/util/extend.ts

@@ -1,8 +1,7 @@
 import { Call, ComposeLeft, Fn, Match, Tuples } from "hotscript"
+import { CommonKeys } from "."
 
 
-type CommonKeys<A, B> = Extract<keyof A, keyof B>
-
 type ExtendReducer<Super, Self> = (
     Pick<Self, CommonKeys<Self, Super>> extends Pick<Super, CommonKeys<Self, Super>>
         ? Omit<Super, CommonKeys<Self, Super>> & Self
@@ -13,7 +12,7 @@ interface ExtendReducerFn extends Fn {
 }
 
 export type ExtendFn = Tuples.Reduce<ExtendReducerFn, {}>
-export type Extend<T extends object[]> = Call<ExtendFn, T>
+export type Extend<T extends {}[]> = Call<ExtendFn, T>
 
 
 export type ExtendableFn = ComposeLeft<[
@@ -23,4 +22,4 @@ export type ExtendableFn = ComposeLeft<[
         Match.With<any, true>,
     ]>
 ]>
-export type Extendable<T extends object[]> = Call<ExtendableFn, T>
+export type Extendable<T extends {}[]> = Call<ExtendableFn, T>

src/util/inheritance.ts

@@ -1,9 +1,5 @@
-/**
- * Represents the common keys between two types.
- * @template A - The first type.
- * @template B - The second type.
- */
-export type CommonKeys<A, B> = Extract<keyof A, keyof B>
+import { CommonKeys } from "."
+
 
 /**
  * Merges an inheritance tree defined by an array of types, considering overrides.

src/util/misc.ts

@@ -2,6 +2,17 @@ import { Fn } from "hotscript"
 import { Simplify } from "type-fest"
 
 
+/**
+ * Represents the common keys between two types.
+ * @template A - The first type.
+ * @template B - The second type.
+ */
+export type CommonKeys<A, B> = Extract<keyof A, keyof B>
+
+export type KeysOnlyInLeft<Left, Right> = {
+    [K in Exclude<keyof Left, keyof Right>]: Left[K]
+}
+
 export interface SimplifyFn extends Fn {
     return: Simplify<this["arg0"]>
 }