import type { google } from '@gcf/firestore-protos';
/**
 * Firestore-compatible evaluation for `StructuredQuery.UnaryFilter`.
 *
 * Semantics captured here:
 * - **IS_NULL**: matches only when the field is present and `null`
 *   (missing/`undefined` does **not** match).
 * - **IS_NAN**: matches only when the field is a `number` and `NaN`.
 * - **IS_NOT_NULL**: matches only when the field is present and **not** `null`
 *   (missing/`undefined` does **not** match).
 * - **IS_NOT_NAN**: matches only when the field is a `number` and **not** `NaN`
 *   (non-numeric values and missing/`undefined` do **not** match).
 *
 * Note: These semantics differ from equality semantics with `null`
 * (e.g., `== null` may include missing), but unary operators here require
 * field **presence** for the non-null variants.
 */
export declare class UnaryOperators {
    /**
     * Evaluates a unary operator against a single value.
     *
     * @param operator - GAPIC unary operator (`IS_NULL`, `IS_NAN`, `IS_NOT_NULL`, `IS_NOT_NAN`).
     * @param value - The field value from the document (may be missing/`undefined`).
     * @returns `true` if the predicate matches; otherwise `false`.
     * @throws {Error} If the operator is not supported.
     */
    static eval(operator: google.firestore.v1.StructuredQuery.UnaryFilter.Operator | null | undefined, value: unknown): boolean;
}
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