src/tests.ts

@@ -1,5 +1,6 @@
-import { AbstractClass } from "type-fest"
+import { AbstractClass, UnionToIntersection } from "type-fest"
 import { expresses, extendsAndExpresses, trait } from "."
+import { ClassesInstances, ClassesInstancesIntersection, ClassesStaticMembers, MergeInheritanceTree, MergeInheritanceTreeWithoutOverriding } from "./util"
 
 
 const Identifiable = <ID>() =>
@@ -92,46 +93,16 @@ class Test3 {
 }
 
 
-type CommonKeys<A, B> = Extract<keyof A, keyof B>
-
-type Extend<T extends readonly any[]> = (
-    T extends [infer Super, infer Self, ...infer Rest]
-        ? Pick<Self, CommonKeys<Self, Super>> extends Pick<Super, CommonKeys<Self, Super>>
-            ? Extend<[
-                Omit<Super, CommonKeys<Self, Super>> & Self,
-                ...Rest,
-            ]>
-            : never
-        : T extends [infer Self]
-            ? Self
-            : "Empty array"
-)
-
-type ClassesInstances<Classes extends readonly any[]> = (
-    Classes extends [infer Class, ...infer Rest]
-        ? Class extends AbstractClass<any>
-            ? [InstanceType<Class>, ...ClassesInstances<Rest>]
-            : never
-        : []
-)
-
-type StaticMembers<Class extends AbstractClass<any>> = (
-    Omit<Class, "prototype">
-)
-
-type ClassesStaticMembers<Classes extends readonly any[]> = (
-    Classes extends [infer Class, ...infer Rest]
-        ? Class extends AbstractClass<any>
-            ? [StaticMembers<Class>, ...ClassesStaticMembers<Rest>]
-            : never
-        : []
-)
-
 type ExtendClasses<Classes extends readonly AbstractClass<any>[]> = (
     AbstractClass<
-        Extend<ClassesInstances<Classes>>
+        // Extend<ClassesInstances<Classes>>
+        MergeInheritanceTreeWithoutOverriding<
+            ClassesInstances<Classes>
+        >
     > &
-    Extend<ClassesStaticMembers<Classes>>
+    MergeInheritanceTree<
+        ClassesStaticMembers<Classes>
+    >
 )
 
 
@@ -140,13 +111,13 @@ type MixedTestProto = ExtendClasses<[
     typeof Test2,
     typeof Test3,
 ]>
-
 declare const MixedTestProto: MixedTestProto
 
-class MixedTest extends MixedTestProto {}
+class MixedTest extends MixedTestProto {
+}
 
 MixedTest.prototype
-new MixedTest().name
+new MixedTest().status.expiresAt
 
 // type MixedTestTraitsProto = Class<
 //     Extend2<TestTrait2, TestTrait1>,

src/util/class.ts

@@ -0,0 +1,66 @@
+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/index.ts

@@ -0,0 +1,2 @@
+export * from "./class"
+export * from "./inheritance"

src/util/inheritance.ts

@@ -0,0 +1,40 @@
+/**
+ * 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>
+
+/**
+ * Merges an inheritance tree defined by an array of types, considering overrides.
+ * @template T - An array of types representing the inheritance tree.
+ */
+export type MergeInheritanceTree<T extends readonly any[]> = (
+    T extends [infer Super, infer Self, ...infer Rest]
+        ? Pick<Self, CommonKeys<Self, Super>> extends Pick<Super, CommonKeys<Self, Super>>
+            ? MergeInheritanceTree<[
+                Omit<Super, CommonKeys<Self, Super>> & Self,
+                ...Rest,
+            ]>
+            : never
+        : T extends [infer Self]
+            ? Self
+            : void
+)
+
+/**
+ * Merges an inheritance tree defined by an array of types without allowing overrides.
+ * @template T - An array of types representing the inheritance tree.
+ */
+export type MergeInheritanceTreeWithoutOverriding<T extends readonly any[]> = (
+    T extends [infer Super, infer Self, ...infer Rest]
+        ? Pick<Self, CommonKeys<Self, Super>> extends Pick<Super, CommonKeys<Self, Super>>
+            ? MergeInheritanceTreeWithoutOverriding<[
+                Super & Self,
+                ...Rest,
+            ]>
+            : never
+        : T extends [infer Self]
+            ? Self
+            : void
+)