/**
 * is() - Checks if a value is an instance of a class
 *
 * We can't use instanceof 'cause that breaks across realms - e.g. when an atom
 * instance is shared between a parent and child window, that instance's object
 * reference will be different in both windows (since each window creates its
 * own copy of Zedux).
 *
 * The classToCheck should have a static $$typeof property whose value is a
 * symbol created with Symbol.for() (sharing the symbol reference across realms)
 *
 * This works no matter how deep the inheritance tree is for either object
 * passed.
 *
 * @param val anything - the thing we're checking
 * @param classToCheck a class with a static $$typeof property
 * @returns boolean - whether val is an instanceof classToCheck
 */
export declare const is: (val: any, classToCheck: {
    $$typeof: symbol;
}) => boolean;