Refactoring

src/trait.ts

@@ -0,0 +1,117 @@
+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
+)