41 lines
1.7 KiB
TypeScript
41 lines
1.7 KiB
TypeScript
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const factorySymbol = Symbol.for("bunny.lazyFactory");
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const cacheSymbol = Symbol("bunny.lazyCache");
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const dummySymbol = Symbol("bunny.lazyDummy");
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const unconfigurable = ["arguments", "caller", "prototype"];
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const isUnconfigurable = (key: PropertyKey) => typeof key === "string" && unconfigurable.includes(key);
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const lazyHandler: ProxyHandler<any> = {
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...Object.fromEntries(Object.getOwnPropertyNames(Reflect).map(fnName => {
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return [fnName, (target: any, ...args: any[]) => {
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// @ts-ignore
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const func = s => Reflect[fnName](s, ...args);
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return func(target[factorySymbol]()) ?? func(target[dummySymbol]);
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}];
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})),
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ownKeys: target => {
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const cacheKeys = Reflect.ownKeys(target[factorySymbol]() ?? target[dummySymbol]);
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unconfigurable.forEach(key => isUnconfigurable(key) && cacheKeys.push(key));
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return cacheKeys;
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},
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getOwnPropertyDescriptor: (target, p) => {
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if (isUnconfigurable(p)) return Reflect.getOwnPropertyDescriptor(target, p);
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const descriptor = Reflect.getOwnPropertyDescriptor(target[factorySymbol]() ?? target[dummySymbol], p);
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if (descriptor) Object.defineProperty(target, p, descriptor);
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return descriptor;
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},
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};
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/**
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* Lazy proxy that will only call the factory function when needed (when a property is accessed)
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* @param factory Factory function to create the object
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* @returns A proxy that will call the factory function only when needed
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*/
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export function proxyLazy<T>(factory: () => T, dummy: any = () => void 0): T {
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dummy[factorySymbol] = () => dummy[cacheSymbol] ??= factory();
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dummy[dummySymbol] = dummy;
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return new Proxy(dummy, lazyHandler) as any;
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}
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