/**
 * Asserts that a value is truthy, throwing an error if it is not.
 *
 * @param value - The value to check.
 * @param message - Optional error message to throw if the assertion fails.
 * @throws Error if the value is falsy.
 *
 * @example
 * ```typescript
 * assert(user !== null, 'User must be defined')
 * ```
 */
export declare function assert(value: unknown, message?: string): asserts value;
/**
 * Conditionally asserts a condition only when a value is defined.
 * Does nothing if the value is undefined or null.
 *
 * @param value - The value to check for definedness.
 * @param condition - The condition to assert if value is defined.
 * @param message - Optional error message to throw if the assertion fails.
 * @throws Error if value is defined and condition is falsy.
 *
 * @example
 * ```typescript
 * assertIfDefined(user, user?.age >= 18, 'User must be an adult')
 * ```
 */
export declare function assertIfDefined(value: unknown, condition: unknown, message?: string): asserts condition;