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/** An iterator that allows peeking at the next item without removing it. */export class Peekable<T, TReturn=unknown, TNext = undefined> implements Iterator<T, TReturn, TNext> {
    static from<T>(inner: Iterable<T>): Peekable<T> {        return new Peekable(inner[Symbol.iterator]())    }        #inner: Iterator<T,TReturn,TNext>;    #peeked?: IteratorResult<T, TReturn>;

    constructor(inner: Iterator<T, TReturn, TNext>) {        this.#inner = inner        this.return = inner.return?.bind(inner)        this.throw = inner.throw?.bind(inner)    }
    /** Returns the value that the next call to {@link #next} would yield. */    peek(): IteratorResult<T, TReturn> {        if (this.#peeked === undefined) {            this.#peeked = this.#inner.next()        }        return this.#peeked;    }
    next(): IteratorResult<T, TReturn> {        if (this.#peeked !== undefined) {            let next = this.#peeked            this.#peeked = undefined            return next        }
        return this.#inner.next()    }
    // Delegate to inner:    return?: ((value?: TReturn) => IteratorResult<T,TReturn>);    throw?: ((e?: unknown) => IteratorResult<T,TReturn>);}



/** An iterator that allows peeking at the next item without removing it. */export class PeekableAsync<T, TReturn=unknown, TNext = undefined> implements AsyncIterator<T, TReturn, TNext> {
    static from<T>(inner: AsyncIterable<T>): PeekableAsync<T> {        return new PeekableAsync(inner[Symbol.asyncIterator]())    }        #inner: AsyncIterator<T,TReturn,TNext>;    #peeked?: Promise<IteratorResult<T, TReturn>>;

    constructor(inner: AsyncIterator<T, TReturn, TNext>) {        this.#inner = inner        this.return = inner.return?.bind(inner)        this.throw = inner.throw?.bind(inner)    }
    /** Returns the value that the next call to {@link #next} would yield. */    peek(): Promise<IteratorResult<T, TReturn>> {        if (this.#peeked === undefined) {            this.#peeked = this.#inner.next()        }        return this.#peeked;    }
    next(): Promise<IteratorResult<T, TReturn>> {        if (this.#peeked !== undefined) {            let next = this.#peeked            this.#peeked = undefined            return next        }
        return this.#inner.next()    }
    // Delegate to inner:    return?: ((value?: TReturn) => Promise<IteratorResult<T,TReturn>>);    throw?: ((e?: unknown) => Promise<IteratorResult<T,TReturn>>);}