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const _arr = new WeakMap<AppendOnlyList<unknown>, unknown>();
export class AppendOnlyList<T> {  constructor() {    _arr.set(this, []);  }  get length(): number {    return (<T[]>_arr.get(this)!).length;  }  toString(): string {    return (<T[]>_arr.get(this)!).toString();  }  toLocaleString(): string {    return (<T[]>_arr.get(this)!).toLocaleString();  }  push(...items: T[]): number {    return (<T[]>_arr.get(this)!).push(...items);  }  entries(): IterableIterator<[number, T]> {    return (<T[]>_arr.get(this)!).entries()  }  keys(): IterableIterator<number> {    return (<T[]>_arr.get(this)!).keys()  }  values(): IterableIterator<T> {    return (<T[]>_arr.get(this)!).values()  }  [Symbol.iterator](): IterableIterator<T> {    return (<T[]>_arr.get(this)!)[Symbol.iterator]();  }  [Symbol.unscopables](): { copyWithin: boolean; entries: boolean; fill: boolean; find: boolean; findIndex: boolean; keys: boolean; values: boolean; } {    throw new Error('Method not implemented.');  }}