/**
 * Check if a value is a string.
 *
 * @example
 * ```ts
 * const val: unknown = "hello";
 * if (isString(val)) {
 *   val.toUpperCase(); // TypeScript knows val is string
 * }
 * ```
 */
export declare function isString(value: unknown): value is string;
/**
 * Check if a value is a number (excludes NaN by default).
 *
 * @example
 * ```ts
 * isNumber(42)      // true
 * isNumber(NaN)     // false
 * isNumber("42")    // false
 * ```
 */
export declare function isNumber(value: unknown): value is number;
/**
 * Check if a value is a number, including NaN.
 */
export declare function isNumberIncludingNaN(value: unknown): value is number;
/**
 * Check if a value is a finite number (excludes NaN and Infinity).
 */
export declare function isFiniteNumber(value: unknown): value is number;
/**
 * Check if a value is a boolean.
 */
export declare function isBoolean(value: unknown): value is boolean;
/**
 * Check if a value is a bigint.
 */
export declare function isBigInt(value: unknown): value is bigint;
/**
 * Check if a value is a symbol.
 */
export declare function isSymbol(value: unknown): value is symbol;
/**
 * Check if a value is null.
 */
export declare function isNull(value: unknown): value is null;
/**
 * Check if a value is undefined.
 */
export declare function isUndefined(value: unknown): value is undefined;
/**
 * Check if a value is null or undefined.
 *
 * @example
 * ```ts
 * if (!isNullish(val)) {
 *   // val is narrowed to exclude null | undefined
 * }
 * ```
 */
export declare function isNullish(value: unknown): value is null | undefined;
/**
 * Check if a value is NOT null and NOT undefined.
 */
export declare function isNonNullish<T>(value: T): value is NonNullable<T>;
/**
 * Check if a value is a function.
 */
export declare function isFunction(value: unknown): value is Function;
/**
 * Check if a value is a primitive type.
 */
export declare function isPrimitive(value: unknown): value is string | number | boolean | bigint | symbol | null | undefined;
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