package.json

@@ -18,6 +18,16 @@
         "types": "./dist/lib.d.cts",
         "default": "./dist/lib.cjs"
       }
+    },
+    "./util": {
+      "import": {
+        "types": "./dist/util.d.mts",
+        "default": "./dist/util.mjs"
+      },
+      "require": {
+        "types": "./dist/util.d.cts",
+        "default": "./dist/util.cjs"
+      }
     }
   },
   "scripts": {
@@ -28,7 +38,8 @@
     "clean:node": "rm -rf node_modules"
   },
   "dependencies": {
-    "type-fest": "^4.10.1"
+    "hotscript": "^1.0.13",
+    "type-fest": "^4.10.2"
   },
   "devDependencies": {
     "@rollup/plugin-node-resolve": "^15.2.3",

rollup.config.ts

@@ -5,17 +5,20 @@ import ts from "rollup-plugin-ts"
 import pkg from "./package.json" assert { type: "json" }
 
 
-export default defineConfig({
-    input: "src/index.ts",
+export const createBundleConfig = (
+    input:  string,
+    name:   keyof typeof pkg.exports,
+) => (
+    defineConfig({
+        input,
 
         output: [
             {
-            file:    pkg.exports["."].import.default,
+                file:    pkg.exports[name].import.default,
                 format:  "esm",
             },
-
             {
-            file:    pkg.exports["."].require.default,
+                file:    pkg.exports[name].require.default,
                 format:  "cjs",
             },
         ],
@@ -31,4 +34,11 @@ export default defineConfig({
                 extensions: ["ts"],
             }),
         ],
-})
+    })
+)
+
+
+export default [
+    createBundleConfig("src/lib.ts", "."),
+    createBundleConfig("src/util/lib.ts", "./util"),
+]

src/Trait.ts

@@ -0,0 +1,153 @@
+import { Fn, Pipe, Tuples } from "hotscript"
+import { AbstractClass, Class, Opaque } from "type-fest"
+import { AbstractTag, TraitExpression, emptyTraitExpression } from "."
+import { ExtendFn, SimplifyFn, StaticMembers, StaticMembersFn } from "./util"
+
+
+export type AddAbstractToImplClass<
+    ImplClass extends Class<{}, []>,
+    Abstract  extends {},
+> = (
+    Class<
+        Abstract & InstanceType<ImplClass>,
+        ConstructorParameters<ImplClass>
+    > &
+    StaticMembers<ImplClass>
+)
+
+export type RemoveAbstractFromImplClass<
+    ImplClassWithAbstract extends Class<Abstract, []>,
+    Abstract              extends {},
+> = (
+    Class<
+        Omit<InstanceType<ImplClassWithAbstract>, keyof Abstract>,
+        ConstructorParameters<ImplClassWithAbstract>
+    > &
+    StaticMembers<ImplClassWithAbstract>
+)
+
+
+export class Trait<
+    Supertraits extends TraitExpression<typeof TraitExpression.NullSuperclass, Trait<any, any, any>[], Trait<any, any, any>[]>,
+    Abstract    extends {},
+    ImplClass   extends Class<{}, []>,
+> {
+    constructor(
+        readonly supertraits:  Supertraits,
+        readonly abstract:     Abstract,
+        readonly apply:        (Super: AbstractClass<{}>) => ImplClass,
+    ) {}
+}
+
+export namespace Trait {
+    export type OwnSupertraits<T> = (
+        T extends Trait<infer Supertraits, any, any>
+            ? Supertraits
+            : never
+    )
+    export interface OwnSupertraitsFn extends Fn {
+        return: Trait.OwnSupertraits<this["arg0"]>
+    }
+
+    export type OwnAbstract<T> = (
+        T extends Trait<any, infer Abstract, any>
+            ? Abstract
+            : never
+    )
+    export interface OwnAbstractFn extends Fn {
+        return: Trait.OwnAbstract<this["arg0"]>
+    }
+
+    export type OwnImplClass<T> = (
+        T extends Trait<any, any, infer ImplClass>
+            ? ImplClass
+            : never
+    )
+    export interface OwnImplClassFn extends Fn {
+        return: Trait.OwnImplClass<this["arg0"]>
+    }
+
+    export type OwnImplInstance<T> = (
+        T extends Trait<any, any, infer ImplClass>
+            ? InstanceType<ImplClass>
+            : never
+    )
+    export interface OwnImplInstanceFn extends Fn {
+        return: Trait.OwnImplInstance<this["arg0"]>
+    }
+
+    export type OwnClass<T> = (
+        T extends Trait<any, infer Abstract, infer ImplClass>
+            ? AddAbstractToImplClass<ImplClass, Abstract>
+            : never
+    )
+    export interface OwnClassFn extends Fn {
+        return: Trait.OwnClass<this["arg0"]>
+    }
+
+    export type OwnInstance<T> = (
+        T extends Trait<any, infer Abstract, infer ImplClass>
+            ? InstanceType<
+                AddAbstractToImplClass<ImplClass, Abstract>
+            >
+            : never
+    )
+    export interface OwnInstanceFn extends Fn {
+        return: Trait.OwnInstance<this["arg0"]>
+    }
+
+    export type Supertraits<T> = (
+        T extends Trait<infer Supertraits, any, any>
+            ? TraitExpression.AllTraits<Supertraits>
+            : never
+    )
+    export interface SupertraitsFn extends Fn {
+        return: Trait.Supertraits<this["arg0"]>
+    }
+
+    export type Class<T> = (
+        AbstractClass<
+            Trait.Instance<T>,
+            any[]
+        > &
+        Pipe<[...Trait.Supertraits<T>, T], [
+            Tuples.Map<Trait.OwnClassFn>,
+            Tuples.Map<StaticMembersFn>,
+            ExtendFn,
+            SimplifyFn,
+        ]>
+    )
+    export interface ClassFn extends Fn {
+        return: Trait.Class<this["arg0"]>
+    }
+
+    export type Instance<T> = (
+        Pipe<[...Trait.Supertraits<T>, T], [
+            Tuples.Map<Trait.OwnInstanceFn>,
+            ExtendFn,
+            SimplifyFn,
+        ]>
+    )
+    export interface InstanceFn extends Fn {
+        return: Trait.Instance<this["arg0"]>
+    }
+}
+
+
+export type TraitApplierSuperTag = "@thilawyn/traitify-ts/TraitApplierSuper"
+
+export function trait<
+    Abstract              extends {},
+    ImplClassWithAbstract extends Class<Abstract, []>,
+>(
+    abstract: Opaque<Abstract, AbstractTag>,
+    apply: (Super: Opaque<AbstractClass<Abstract>, TraitApplierSuperTag>) => (
+        Opaque<ImplClassWithAbstract, TraitApplierSuperTag>
+    ),
+) {
+    return new Trait(
+        emptyTraitExpression,
+        abstract as Abstract,
+        apply    as any as (Super: AbstractClass<{}>) => RemoveAbstractFromImplClass<ImplClassWithAbstract, Abstract>,
+    )
+}

src/TraitExpression.ts

@@ -0,0 +1,117 @@
+import { Call, Fn, Pipe, Tuples } from "hotscript"
+import { AbstractClass, Class, Opaque } from "type-fest"
+import { AbstractTag, RemoveAbstractFromImplClass, Trait, TraitApplierSuperTag } from "."
+import { ExtendFn, SimplifyFn, StaticMembersFn } from "./util"
+
+
+// type RemoveSupertraitsAbstractFromAbstract<Left, Right> = {
+//     [Key in Extract<keyof Left, keyof Right>]: Left[Key]
+// } & {
+//     [Key in Exclude<keyof Left, keyof Right>]: Left[Key]
+// }
+
+
+export class TraitExpression<
+    Superclass extends AbstractClass<{}>,
+    OwnTraits  extends Trait<any, any, any>[],
+    AllTraits  extends Trait<any, any, any>[],
+> {
+    constructor(
+        readonly superclass:  Superclass,
+        readonly ownTraits:   OwnTraits,
+        readonly allTraits:   AllTraits,
+    ) {}
+
+    get extends(): (
+        AbstractClass<
+            Pipe<[
+                InstanceType<Superclass>,
+                ...Call<Tuples.Map<Trait.OwnImplInstanceFn>, AllTraits>,
+            ], [
+                ExtendFn,
+                SimplifyFn,
+            ]>,
+
+            ConstructorParameters<Superclass>
+        > &
+
+        Pipe<[
+            Superclass,
+            ...Call<Tuples.Map<Trait.OwnImplClassFn>, AllTraits>,
+        ], [
+            Tuples.Map<StaticMembersFn>,
+            ExtendFn,
+            SimplifyFn,
+        ]>
+    ) {
+        return this.allTraits.reduce(
+            (previous, trait) => trait.apply(previous),
+            this.superclass as Opaque<Superclass, TraitApplierSuperTag>,
+        ) as any
+    }
+
+    subtrait<
+        SubtraitAbstract              extends Implements<typeof this>,
+        SubtraitImplClassWithAbstract extends Class<SubtraitAbstract, []>,
+    >(
+        abstract: (expression: typeof this) => Opaque<SubtraitAbstract, AbstractTag>,
+        apply: (Super: Opaque<AbstractClass<SubtraitAbstract>, TraitApplierSuperTag>) => (
+            Opaque<SubtraitImplClassWithAbstract, TraitApplierSuperTag>
+        ),
+    ) {
+        return new Trait(
+            this,
+            // {} as RemoveSupertraitsAbstractFromAbstract<SubtraitAbstract, Implements<typeof this>>,
+            {} as SubtraitAbstract,  // TODO: find a way to cleanly substract Implements<typeof this> from this.
+            apply as any as (Super: AbstractClass<{}>) => RemoveAbstractFromImplClass<SubtraitImplClassWithAbstract, SubtraitAbstract>,
+        )
+    }
+}
+
+export namespace TraitExpression {
+    export class NullSuperclass {}
+
+    export type Superclass<T> = (
+        T extends TraitExpression<infer Superclass, any, any>
+            ? Superclass
+            : never
+    )
+    export interface SuperclassFn extends Fn {
+        return: TraitExpression.Superclass<this["arg0"]>
+    }
+
+    export type OwnTraits<T> = (
+        T extends TraitExpression<any, infer OwnTraits, any>
+            ? OwnTraits
+            : never
+    )
+    export interface OwnTraitsFn extends Fn {
+        return: TraitExpression.OwnTraits<this["arg0"]>
+    }
+
+    export type AllTraits<T> = (
+        T extends TraitExpression<any, any, infer AllTraits>
+            ? AllTraits
+            : never
+    )
+    export interface AllTraitsFn extends Fn {
+        return: TraitExpression.AllTraits<this["arg0"]>
+    }
+}
+
+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>
+        ? Pipe<AllTraits, [
+            Tuples.Map<Trait.OwnAbstractFn>,
+            ExtendFn,
+            SimplifyFn,
+        ]>
+        : never
+)

src/TraitExpressionBuilder.ts

@@ -0,0 +1,131 @@
+import { Call, Fn, Pipe, Tuples } from "hotscript"
+import { AbstractClass } from "type-fest"
+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>[],
+    AllTraits extends Trait<any, any, any>[],
+> {
+    constructor(private expression: TraitExpression<Super, OwnTraits, AllTraits>) {}
+
+    extends<
+        Super extends AbstractClass<any>
+    >(
+        superclass: Super
+    ) {
+        return new TraitExpressionBuilder(
+            new TraitExpression(
+                superclass,
+                this.expression.ownTraits,
+                this.expression.allTraits,
+            )
+        )
+    }
+
+    expresses<
+        Traits extends Trait<any, any, any>[]
+    >(
+        ...traits: Traits
+    ): TraitExpressionBuilder<
+        Super,
+        [...OwnTraits, ...Traits],
+        [...AllTraits, ...SpreadSupertraits<Traits>]
+    > {
+        return new TraitExpressionBuilder(
+            new TraitExpression(
+                this.expression.superclass,
+                [...this.expression.ownTraits, ...traits] as const,
+                [...this.expression.allTraits, ...this.spreadSupertraits(traits)] as const,
+            )
+        ) as any
+    }
+
+    private spreadSupertraits<
+        Traits extends Trait<
+            TraitExpression<any, any, Trait<any, any, any>[]>,
+            any,
+            any
+        >[]
+    >(
+        traits: Traits
+    ) {
+        return traits.flatMap(trait => [
+            ...trait.supertraits.allTraits,
+            trait,
+        ]) as SpreadSupertraits<Traits>
+    }
+
+    build() {
+        return this.expression as BuildTraitExpression<Super, OwnTraits, AllTraits>
+    }
+
+    then<V>(fn: (expression: ReturnType<typeof this.build>) => V): V {
+        return fn(this.build())
+    }
+}
+
+export const expression = new TraitExpressionBuilder(emptyTraitExpression)

src/abstract.ts

@@ -0,0 +1,10 @@
+import { Opaque } from "type-fest"
+
+
+export type AbstractTag = "@thilawyn/traitify-ts/Abstract"
+
+export function abstract<
+    Abstract extends {} = {}
+>() {
+    return {} as Opaque<Abstract, AbstractTag>
+}

src/expresses.ts

@@ -1,84 +0,0 @@
-import { AbstractClass, Opaque } from "type-fest"
-import { Trait, TraitApplierSuperTag } from "."
-import { ClassesInstances, ClassesStaticMembers, MergeInheritanceTree, MergeInheritanceTreeWithoutOverriding, StaticMembers, TraitsClasses } from "./util"
-
-
-/**
- * Extends a class with the given traits and expresses their combined functionality.
- * @template C - The abstract class type.
- * @template Traits - An array of traits.
- * @param extend - The class to extend.
- * @param traits - An array of traits to apply.
- * @returns A new class type expressing the combined functionality of the base class and traits.
- * @example
- * Extends a superclass and applies traits:
- * ```ts
- * class User extends extendsAndExpresses(Entity,
- *     Identifiable<bigint>(),
- *     Permissible,
- * ) {
- *     readonly id: bigint
- *
- *     constructor(id: bigint) {
- *         super()
- *         this.id = id
- *     }
- * }
- * ```
- */
-export function extendsAndExpresses<
-    C      extends AbstractClass<any>,
-    Traits extends readonly Trait<any>[],
->(
-    extend: C,
-    ...traits: Traits
-) {
-    return traits.reduce(
-        (previous, trait) => trait(previous),
-        extend as Opaque<C, TraitApplierSuperTag>,
-    ) as unknown as (
-        AbstractClass<
-            MergeInheritanceTreeWithoutOverriding<[
-                InstanceType<C>,
-                ...ClassesInstances<
-                    TraitsClasses<Traits>
-                >,
-            ]>,
-
-            ConstructorParameters<C>
-        > &
-
-        MergeInheritanceTree<[
-            StaticMembers<C>,
-            ...ClassesStaticMembers<
-                TraitsClasses<Traits>
-            >,
-        ]>
-    )
-}
-
-/**
- * Expresses the combined functionality of multiple traits.
- * @template Traits - An array of trait.
- * @param traits - An array of trait to apply.
- * @returns A new class type expressing the combined functionality of the traits.
- * @example
- * Applies traits to a class:
- * ```ts
- * class User extends expresses(Identifiable<bigint>(), Permissible) {
- *     readonly id: bigint
- *
- *     constructor(id: bigint) {
- *         super()
- *         this.id = id
- *     }
- * }
- * ```
- */
-export function expresses<
-    Traits extends readonly Trait<any>[],
->(
-    ...traits: Traits
-) {
-    return extendsAndExpresses(Object, ...traits)
-}

src/index.ts

@@ -1,2 +1,4 @@
-export * from "./expresses"
-export * from "./trait"
+export * from "./Trait"
+export * from "./TraitExpression"
+export * from "./TraitExpressionBuilder"
+export * from "./abstract"

src/lib.ts

@@ -0,0 +1,6 @@
+export {
+    abstract, expression, trait,
+    type Implements,
+    type Trait,
+    type TraitExpression
+} from "."

src/tests.ts

@@ -1,131 +1,81 @@
-import { AbstractClass } from "type-fest"
-import { expresses, extendsAndExpresses, trait } from "."
-import { ClassesInstances, MergeInheritanceTree } from "./util"
+import { Simplify } from "type-fest"
+import { Implements, Trait, abstract, expression, trait } from "."
+import { Pipe } from "hotscript"
 
 
-const Identifiable = <ID>() =>
-    trait(Super => {
-        abstract class Identifiable extends Super {
-            abstract readonly id: ID
+const PrintsHelloOnNew = trait(
+    abstract(),
+    Super => class PrintsHelloOnNew extends Super {
+        constructor(...args: any[]) {
+            super(...args)
+            console.log("Hello!")
+        }
+    },
+)
 
+const Identifiable = <ID>() => trait(
+    abstract<{ readonly id: ID }>(),
+    Super => class Identifiable extends Super {
         equals(el: Identifiable) {
             return this.id === el.id
         }
-
-            constructor(...args: any[]) {
-                super(...args)
-                console.log("Identified constructor")
-            }
-        }
-
-        return Identifiable
-    })
-
-const ImplementsIdentifiable = <ID>(defaultID: ID) =>
-    trait(Super => {
-        abstract class ImplementsIdentifiable extends extendsAndExpresses(
-            Super,
-            Identifiable<ID>(),
-        ) {
-            id: ID = defaultID
-
-            constructor(...args: any[]) {
-                super(...args)
-                console.log("ImplementsIdentifiable constructor")
-            }
-        }
-
-        return ImplementsIdentifiable
-    })
-
-
-const Permissible = trait(Super => {
-    abstract class Permissible extends Super {
-        static readonly defaultPermissions: string[] = []
-        permissions: string[] = []
-
-        constructor(...args: any[]) {
-            super(...args)
-            console.log("Permissible constructor")
-        }
-    }
-
-    return Permissible
-})
-
-
-const UserProto = expresses(
-    // Identifiable<bigint>(),
-    ImplementsIdentifiable(0n),
-    Permissible,
+    },
 )
 
-class User extends UserProto {
-    constructor(id: bigint) {
-        super()
-        this.id = id
-    }
-}
-
-const user1 = new User(1n)
-console.log(user1)
-console.log(user1.equals(user1))
-
-
-const Test1 = trait(Super => {
-    abstract class Test1 extends Super {
-        declare static name: string
-        declare static testValue: (
-            { _tag: "type1", value: string } |
-            { _tag: "type2", value: number }
-        )
-
-        abstract name: string
-
-        declare createdAt: Date
-        declare readonly status: (
+const StatefulSubscription = trait(
+    abstract<{
+        readonly isStatefulSubscription: true
+        readonly status: (
             { _tag: "awaitingPayment" } |
             { _tag: "active", activeSince: Date, expiresAt?: Date } |
             { _tag: "expired", expiredSince: Date }
         )
+    }>(),
+
+    Super => class StatefulSubscription extends Super {},
+)
+
+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 }
             }
 
-    return Test1
-})
+            return abstract<IActiveStatefulSubscription>()
+        },
 
-const Test2 = trait(Super => {
-    abstract class Test2 extends Super {
-        declare readonly status: { _tag: "active", activeSince: Date, expiresAt?: Date }
-    }
+        Super => class ActiveStatefulSubscription extends Super {},
+    )
 
-    return Test2
-})
-
-const Test3 = trait(Super => {
-    abstract class Test3 extends Super {
-        declare static testValue: { _tag: "type2", value: number }
-        declare lol: 10n
-    }
-
-    return Test3
-})
-
-const TestObjectProto = expresses(Test1, Test2, Test3)
-TestObjectProto.testValue
+type T = Trait.Instance<typeof ActiveStatefulSubscription>
 
 
-interface Gneugneu {
-    ahi: string
-    get adolf(): string
+class TestSuperclass {
+    // id: number = 69
+    // static test = 69
 }
 
-class GneugneuImpl implements Gneugneu {
-    ahi: string = ""
-    get adolf(): string {
-        throw new Error("Method not implemented.")
-    }
+const exp = expression
+    .extends(TestSuperclass)
+    .expresses(
+        PrintsHelloOnNew,
+        Identifiable<bigint>(),
+        // Identifiable<number>(),
+        ActiveStatefulSubscription,
+    )
+    .build()
 
+type Abs = Implements<typeof exp>
+
+class User extends exp.extends implements Implements<typeof exp> {
+    readonly isStatefulSubscription: true = true
+    readonly isActiveStatefulSubscription: true = true
+    declare status: { _tag: "active"; activeSince: Date; expiresAt?: Date | undefined }
+    id: bigint = -1n
 }
 
-abstract class Issou extends GneugneuImpl implements Gneugneu {
-}
+console.log(new User())

src/trait.ts

@@ -1,117 +0,0 @@
-import { AbstractClass, AbstractConstructor, Opaque } from "type-fest"
-
-
-/**
- * Represents a trait that can be applied to a class.
- * @template C - The abstract class type.
- */
-export type Trait<
-    C extends AbstractClass<any>
-> = Opaque<
-    TraitApplier<C>,
-    "@thilawyn/thilatrait/Trait"
->
-
-export type TraitApplierSuperTag = "@thilawyn/thilatrait/Super"
-
-/**
- * Represents the function signature for applying a trait to a parent class.
- * @template C - The abstract class type.
- */
-export type TraitApplier<
-    C extends AbstractClass<any>
-> = (
-    (Super: Opaque<AbstractConstructor<object>, TraitApplierSuperTag>) => Opaque<C, TraitApplierSuperTag>
-)
-
-/**
- * Creates a trait using the provided trait applier function.
- * @template C - The abstract class type.
- * @param applier - The trait applier function.
- * @returns A trait.
- * @example
- * Creates a trait:
- * ```ts
- * const Permissible = trait(Super => {
- *     abstract class Permissible extends Super {
- *         static readonly defaultPermissions: string[] = []
- *         permissions: string[] = []
- *
- *         // Constructor is optional
- *         // If you wish to use it, make sure it takes any[] as an args array and passes it to the super call. This is necessary for inheritance to work properly.
- *         // Trait constructors cannot have typed arguments of their own, they only serve to run logic during object instantiation.
- *         constructor(...args: any[]) {
- *             super(...args)
- *         }
- *     }
- *
- *     return Permissible
- * })
- * ```
- * Creates a generic trait:
- * ```ts
- * const Identifiable = <ID>() =>
- *     trait(Super => {
- *         abstract class Identifiable extends Super {
- *             abstract readonly id: ID
- *
- *             equals(el: Identifiable) {
- *                 return this.id === el.id
- *             }
- *
- *             // Optional
- *             constructor(...args: any[]) {
- *                 super(...args)
- *             }
- *         }
- *
- *         return Identifiable
- *     })
- * ```
- * Creates a subtrait:
- * ```ts
- * const ImplementsIdentifiable = <ID>(defaultID: ID) =>
- *     trait(Super => {
- *         abstract class ImplementsIdentifiable extends extendsAndExpresses(
- *             Super,
- *             Identifiable<ID>(),
- *         ) {
- *             id: ID = defaultID
- *
- *             // Optional
- *             constructor(...args: any[]) {
- *                 super(...args)
- *             }
- *         }
- *
- *         return ImplementsIdentifiable
- *     })
- * ```
- */
-export function trait<
-    C extends AbstractClass<any>
->(
-    applier: TraitApplier<C>
-) {
-    return applier as Trait<C>
-}
-
-/**
- * Returns the class type of a trait.
- * @template T - The trait type.
- */
-export type TraitClass<T> = (
-    T extends Trait<infer C>
-        ? C
-        : never
-)
-
-/**
- * Returns the instance type of a trait.
- * @template T - The trait type.
- */
-export type TraitInstance<T> = (
-    T extends Trait<infer C>
-        ? InstanceType<C>
-        : never
-)

src/util/class.ts

@@ -1,66 +0,0 @@
-import { AbstractClass } from "type-fest"
-
-
-/**
- * Represents an array of instances corresponding to the provided classes.
- * @template Classes - An array of classes extending AbstractClass.
- */
-export type ClassesInstances<Classes extends readonly AbstractClass<any>[]> = (
-    Classes extends [infer Class, ...infer Rest]
-        ? Class extends AbstractClass<any>
-            ? Rest extends AbstractClass<any>[]
-                ? [InstanceType<Class>, ...ClassesInstances<Rest>]
-                : never
-            : never
-        : []
-)
-
-/**
- * Represents an intersection of instances of the provided classes.
- * @template Classes - An array of classes extending AbstractClass.
- */
-export type ClassesInstancesIntersection<Classes extends readonly AbstractClass<any>[]> = (
-    Classes extends [infer Class, ...infer Rest]
-        ? Class extends AbstractClass<any>
-            ? Rest extends AbstractClass<any>[]
-                ? InstanceType<Class> & ClassesInstancesIntersection<Rest>
-                : never
-            : never
-        : {}
-)
-
-/**
- * Represents the static members of a class.
- * @template Class - A class extending AbstractClass.
- */
-export type StaticMembers<Class extends AbstractClass<any>> = (
-    Omit<Class, "prototype">
-)
-
-/**
- * Represents an array of static members corresponding to the provided classes.
- * @template Classes - An array of classes extending AbstractClass.
- */
-export type ClassesStaticMembers<Classes extends readonly AbstractClass<any>[]> = (
-    Classes extends [infer Class, ...infer Rest]
-        ? Class extends AbstractClass<any>
-            ? Rest extends AbstractClass<any>[]
-                ? [StaticMembers<Class>, ...ClassesStaticMembers<Rest>]
-                : never
-            : never
-        : []
-)
-
-/**
- * Represents an intersection of static members of the provided classes.
- * @template Classes - An array of classes extending AbstractClass.
- */
-export type ClassesStaticMembersIntersection<Classes extends readonly AbstractClass<any>[]> = (
-    Classes extends [infer Class, ...infer Rest]
-        ? Class extends AbstractClass<any>
-            ? Rest extends AbstractClass<any>[]
-                ? StaticMembers<Class> & ClassesStaticMembersIntersection<Rest>
-                : never
-            : never
-        : {}
-)

src/util/extend.ts

@@ -0,0 +1,25 @@
+import { Call, ComposeLeft, Fn, Match, Tuples } from "hotscript"
+import { CommonKeys } from "."
+
+
+type ExtendReducer<Super, Self> = (
+    Pick<Self, CommonKeys<Self, Super>> extends Pick<Super, CommonKeys<Self, Super>>
+        ? Omit<Super, CommonKeys<Self, Super>> & Self
+        : never
+)
+interface ExtendReducerFn extends Fn {
+    return: ExtendReducer<this["arg0"], this["arg1"]>
+}
+
+export type ExtendFn = Tuples.Reduce<ExtendReducerFn, {}>
+export type Extend<T extends {}[]> = Call<ExtendFn, T>
+
+
+export type ExtendableFn = ComposeLeft<[
+    ExtendFn,
+    Match<[
+        Match.With<never, false>,
+        Match.With<any, true>,
+    ]>
+]>
+export type Extendable<T extends {}[]> = Call<ExtendableFn, T>

src/util/index.ts

@@ -1,3 +1,3 @@
-export * from "./class"
+export * from "./extend"
 export * from "./inheritance"
-export * from "./trait"
+export * from "./misc"

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/lib.ts

@@ -0,0 +1,6 @@
+export {
+    Extend,
+    ExtendFn,
+    Extendable,
+    ExtendableFn
+} from "."

src/util/misc.ts

@@ -0,0 +1,25 @@
+import { Fn } from "hotscript"
+import { AbstractClass, 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 interface SimplifyFn extends Fn {
+    return: Simplify<this["arg0"]>
+}
+
+/**
+ * Represents the static members of a class.
+ * @template Class - A class extending AbstractClass.
+ */
+export type StaticMembers<Class extends AbstractClass<any>> = (
+    Omit<Class, "prototype">
+)
+export interface StaticMembersFn extends Fn {
+    return: StaticMembers<this["arg0"]>
+}

src/util/trait.ts

@@ -1,16 +0,0 @@
-import { Trait, TraitClass } from ".."
-
-
-/**
- * Represents an array of classes corresponding to the provided traits.
- * @template Traits - An array of traits extending Trait<any>.
- */
-export type TraitsClasses<Traits extends readonly Trait<any>[]> = (
-    Traits extends [infer T, ...infer Rest]
-        ? T extends Trait<any>
-            ? Rest extends Trait<any>[]
-                ? [TraitClass<T>, ...TraitsClasses<Rest>]
-                : never
-            : never
-        : []
-)