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July 21, 2023 14:40
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WIP after playing around in GPT.
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| type Constructor<T> = new (...args: any[]) => T; | |
| type DefaultType<T> = T extends Constructor<infer U> ? U : T; | |
| function defaultObject<V, K extends string | symbol = string | symbol>(Type: Constructor<V> | V): Record<K, DefaultType<V>> & Iterable<[K, DefaultType<V>]> { | |
| const store = new Map<K, DefaultType<V>>(); | |
| const iterable = { | |
| *[Symbol.iterator] () { | |
| for (let [key, value] of store) { | |
| yield [key, value]; | |
| } | |
| } | |
| }; | |
| return new Proxy(iterable as Record<K, DefaultType<V>>, { | |
| get(target: Record<K, DefaultType<V>>, property: K): DefaultType<V> { | |
| if (!store.has(property)) { | |
| if (typeof Type === 'function') { | |
| store.set(property, new (Type as Constructor<V>)() as DefaultType<V>); | |
| } else { | |
| store.set(property, Type as DefaultType<V>); | |
| } | |
| } | |
| return store.get(property)!; | |
| }, | |
| has(target: Record<K, DefaultType<V>>, property: K): boolean { | |
| return store.has(property); | |
| }, | |
| ownKeys(): (string | symbol)[] { | |
| return Array.from(store.keys()); | |
| }, | |
| deleteProperty(target: Record<K, DefaultType<V>>, property: K): boolean { | |
| return store.delete(property); | |
| }, | |
| set(target: Record<K, DefaultType<V>>, property: K, value: DefaultType<V>): boolean { | |
| if (typeof Type === 'function') { | |
| if (!(value instanceof (Type as Constructor<V>))) { | |
| throw new Error(`Value does not belong to the default type.`); | |
| } | |
| } else { | |
| if (value !== Type) { | |
| throw new Error(`Value does not match the default value.`); | |
| } | |
| } | |
| store.set(property, value); | |
| return true; | |
| }, | |
| getOwnPropertyDescriptor(target: Record<K, DefaultType<V>>, property: K) { | |
| if (store.has(property)) { | |
| return { | |
| enumerable: true, | |
| configurable: true, | |
| value: store.get(property), | |
| }; | |
| } | |
| return undefined; | |
| } | |
| }) as Record<K, DefaultType<V>> & Iterable<[K, DefaultType<V>]>; | |
| } | |
| // Usage with Array | |
| const d = defaultObject(Array); | |
| d['abc'].push('def'); | |
| const abc = d['abc']; | |
| console.log('abc' in d); // Outputs: true | |
| for (const [key, value] of d) { | |
| console.log(key, value); | |
| } | |
| delete d['abc']; | |
| console.log('abc' in d); // Outputs: false | |
| // Usage with Set | |
| const s = defaultObject(Set); | |
| s['abc'].add('def'); | |
| console.log('abc' in s); // Outputs: true | |
| for (const [key, value] of s) { | |
| console.log(key, value); | |
| } | |
| delete s['abc']; | |
| console.log('abc' in s); // Outputs: false | |
| // Usage with number | |
| const n = defaultObject(0); | |
| n['abc']++; | |
| console.log('abc' in n); // Outputs: true | |
| for (const [key, value] of n) { | |
| console.log(key, value); | |
| } | |
| delete n['abc']; | |
| console.log('abc' in n); // Outputs: false | |
| // Usage with type checking on set | |
| try { | |
| d['abc'] = 'def'; // Throws an error | |
| } catch (err) { | |
| console.error(err); | |
| } |
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