import { ValidationFailure } from '../error';
import { Validator } from '../interface';
export declare class Sentinel<T, S> implements Validator<T, S | null | undefined> {
    readonly label: string;
    readonly value: T;
    readonly item: Validator<T, S>;
    constructor(label: string, value: T, item: Validator<T, S>);
    cast(value: unknown): ValidationFailure | T;
    validate(value: unknown): ValidationFailure | undefined;
    phantom(): S | null | undefined;
}
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