Created
November 22, 2023 15:20
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Using Proxy and extensive abuse of #private we implement multiple inheritance in typescript
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function Multi<Left extends new (...args: any[]) => object, Right extends new (...args: any[]) => object, Largs extends any[], Rargs extends any[], Linst extends object, Rinst extends object>(Left: Left & (new (...args: Largs) => Linst), Right: Right & (new (...args: Rargs) => Rinst)): { | |
new (largs: Largs, rargs: Rargs): Linst & Rinst | |
} & { [P in keyof Left]: Left[P] } & { [P in keyof Right]: Right[P] } { | |
let proxy; | |
class Multi extends (Left as any) { | |
#bastard: Rinst; | |
constructor(largs: Largs, rargs: Rargs) { | |
super(...largs); | |
this.#bastard = new Right(...rargs); | |
return new Proxy(this, Multi.#handler); | |
} | |
static #handler: ProxyHandler<Multi> = { | |
getPrototypeOf: (target) => { throw "forbidden multi" }, | |
setPrototypeOf: (target, v) => { throw "forbidden multi" }, | |
isExtensible: (target) => Reflect.isExtensible(target) || Reflect.isExtensible(target.#bastard), | |
preventExtensions: (target) => (Reflect.preventExtensions(target), Reflect.preventExtensions(target.#bastard)), | |
getOwnPropertyDescriptor: (target, p) => Reflect.getOwnPropertyDescriptor(target, p) ?? Reflect.getOwnPropertyDescriptor(target.#bastard, p), | |
defineProperty: (target, p, attributes) => +Reflect.defineProperty(target, p, attributes) + +Reflect.defineProperty(target.#bastard, p, attributes) > 0, | |
has: (target, p) => Reflect.has(target, p) || Reflect.has(target.#bastard, p), | |
get: (target, p, receiver) => Reflect.has(target, p) ? Reflect.get(target, p, receiver) : Reflect.get(target.#bastard, p, receiver), | |
set: (target, p, value, receiver) => +Reflect.set(target, p, value, receiver) + +Reflect.set(target.#bastard, p, value, receiver) > 0, | |
deleteProperty: (target, p) => Reflect.deleteProperty(target, p) || Reflect.deleteProperty(target.#bastard, p), | |
ownKeys: (target) => Reflect.ownKeys(target).concat(Reflect.ownKeys(target.#bastard)), | |
}; | |
static #right = Right; | |
static #proxy = proxy = new Proxy(this, { | |
isExtensible: (target) => Reflect.isExtensible(target) || Reflect.isExtensible(target.#right), | |
preventExtensions: (target) => (Reflect.preventExtensions(target), Reflect.preventExtensions(target.#right)), | |
getOwnPropertyDescriptor: (target, p) => Reflect.getOwnPropertyDescriptor(target, p) ?? Reflect.getOwnPropertyDescriptor(target.#right, p), | |
defineProperty: (target, p, attributes) => +Reflect.defineProperty(target, p, attributes) + +Reflect.defineProperty(target.#right, p, attributes) > 0, | |
has: (target, p) => Reflect.has(target, p) || Reflect.has(target.#right, p), | |
get: (target, p, receiver) => Reflect.has(target, p) ? Reflect.get(target, p, receiver) : Reflect.get(target.#right, p, receiver), | |
set: (target, p, value, receiver) => +Reflect.set(target, p, value, receiver) + +Reflect.set(target.#right, p, value, receiver) > 0, | |
deleteProperty: (target, p) => Reflect.deleteProperty(target, p) || Reflect.deleteProperty(target.#right, p), | |
ownKeys: (target) => Reflect.ownKeys(target).concat(Reflect.ownKeys(target.#right)), | |
}) | |
}; | |
return proxy as never; | |
} | |
class Stupid { x = 1; static x = "x" } | |
class Evil { y = 2; static y = "y" } | |
class Foo extends Multi(Stupid, Evil) {} | |
const foo = new Foo([], []); | |
console.log(foo.x, foo.y, Foo.x, Foo.y) |
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