/**
 * A conditional type for a primitive value.
 *
 * @since v0.4.0
 */
export type InputPrimitive<T> = T extends string | number | boolean | null | undefined ? T | string | number | boolean | null | undefined : never;
/**
 * An array of input values `T`.
 *
 * @since v0.4.0
 */
export type InputArray<T> = Input<T>[];
/**
 * An input object type.
 *
 * @since v0.4.0
 */
export type InputObject<T> = {
    [P in keyof T]?: Input<T[P]> | null;
};
/**
 * A recursive type that shows that a given value of type `T` has not yet been validated.
 *
 * @since v0.4.0
 */
export type Input<T> = (T extends (infer U)[] ? InputArray<U> : T extends object ? InputObject<T> : InputPrimitive<T>) | null | undefined;
/**
 * Marks a given `value` as an {@linkcode Input}.
 *
 * @since v0.4.0
 */
export declare function input<T>(value: unknown): Input<T>;
/**
 * If a given `value` is a string, returns the `value`.
 * Otherwise, returns `undefined`.
 *
 * @since v0.4.0
 */
export declare function stringInput(input: unknown): string | undefined;
/**
 * If a given `value` is a number, returns the `value`.
 * Otherwise, returns `undefined`.
 *
 * @since v0.4.0
 */
export declare function numberInput(input: unknown): number | undefined;
/**
 * If a given `value` is a boolean, returns the `value`.
 * Otherwise, returns `undefined`.
 *
 * @since v0.4.0
 */
export declare function booleanInput(input: unknown): boolean | undefined;
/**
 * If a given `value` is an array, returns the `value`.
 * Otherwise, returns `undefined`.
 *
 * @since v0.4.0
 */
export declare function arrayInput<T>(input: unknown): Input<T>[] | undefined;
/**
 * If a given `value` is a non-array object, returns the `value`.
 * Otherwise, returns `undefined`.
 *
 * @since v0.4.0
 */
export declare function objectInput<T>(input: unknown): InputObject<T> | undefined;
/**
 * If a given `value` is null, returns the `value`.
 * Otherwise, returns `undefined`.
 *
 * @since v0.4.0
 */
export declare function nullInput(input: unknown): null | undefined;