import type { Guard } from '../utils/types.js';
/**
 * Assert that a condition is true. Throws `AssertionError` if false.
 * Narrows the condition to `true` in the subsequent code.
 *
 * @example
 * ```ts
 * assert(user !== null, 'User must exist');
 * user.name; // OK — TypeScript knows user is not null
 * ```
 */
export declare function assert(condition: unknown, message?: string): asserts condition;
/**
 * Assert that a value is defined (not undefined).
 * Narrows away `undefined`.
 *
 * @example
 * ```ts
 * const val: string | undefined = getConfig('key');
 * assertDefined(val, 'Config key is required');
 * val.toUpperCase(); // OK
 * ```
 */
export declare function assertDefined<T>(value: T, message?: string): asserts value is Exclude<T, undefined>;
/**
 * Assert that a value is not null and not undefined.
 * Narrows away `null | undefined`.
 *
 * @example
 * ```ts
 * assertNonNull(result);
 * result.doSomething(); // OK
 * ```
 */
export declare function assertNonNull<T>(value: T, message?: string): asserts value is NonNullable<T>;
/**
 * Assert that a value passes a type guard.
 * Narrows to the guarded type.
 *
 * @example
 * ```ts
 * assertType(input, isString, 'Expected string input');
 * input.toUpperCase(); // OK — narrowed to string
 * ```
 */
export declare function assertType<T>(value: unknown, guard: Guard<T>, message?: string): asserts value is T;
/**
 * Assert that a value is truthy.
 * Narrows away falsy values (false, 0, '', null, undefined, NaN).
 */
export declare function assertTruthy<T>(value: T, message?: string): asserts value is NonNullable<T>;
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