/** A resolve/reject callback used within PromiseEx. */
export type PromiseExSubFunc<T, TResult = T> = (value: T) => TResult;
/** The executor function passed to the PromiseEx constructor. */
export type PromiseExFunc<T> = (resolve?: PromiseExSubFunc<T, void>, reject?: PromiseExSubFunc<T, void>) => void;
/** A callback that inspects the attached value and returns whether to cancel the promise. */
export type PromiseExValueFunc<V> = (value?: V) => boolean;
/**
 * An extended Promise that carries an optional attached value and supports cancellation.
 * The value can be inspected via the `then` or `value` methods to conditionally cancel.
 */
export declare class PromiseEx<T, V = void> extends Promise<T> {
    /** Whether the promise has been cancelled via a value callback. */
    cancelled?: boolean;
    private _value?;
    constructor(func: PromiseExFunc<T>, value?: V);
    then<TResult1 = T, TResult2 = never>(onfulfilled?: ((value: T) => TResult1 | PromiseLike<TResult1>) | null | undefined, onrejected?: ((reason: unknown) => TResult2 | PromiseLike<TResult2>) | null | undefined, onvalue?: (value?: V) => boolean): Promise<TResult1 | TResult2>;
    /**
     * Inspects the attached value via the callback; if it returns true, marks the promise as cancelled.
     * @param onvalue - A callback that receives the attached value and returns whether to cancel.
     * @returns This instance for chaining.
     */
    value(onvalue?: (value?: V) => boolean): this;
}
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