/**
 * The `SubtreeRetainer` class keeps track of a number of pieces of data,
 * comparing the values of these pieces at every iteration.
 *
 * This is useful for preventing redraws to relatively static (or huge)
 * components whose VDOM only depends on very few values, when none of them
 * have changed.
 *
 * @example
 * // Check two callbacks for changes on each update
 * this.subtree = new SubtreeRetainer(
 *   () => this.attrs.post.freshness,
 *   () => this.showing
 * );
 *
 * // Add more callbacks to be checked for updates
 * this.subtree.check(() => this.attrs.user.freshness);
 *
 * // In a component's onbeforeupdate() method:
 * return this.subtree.needsRebuild()
 *
 * @see https://mithril.js.org/lifecycle-methods.html#onbeforeupdate
 */
export default class SubtreeRetainer {
    protected callbacks: (() => any)[];
    protected data: Record<string, any>;
    /**
     * @param callbacks Functions returning data to keep track of.
     */
    constructor(...callbacks: (() => any)[]);
    /**
     * Return whether any data has changed since the last check.
     * If so, Mithril needs to re-diff the vnode and its children.
     */
    needsRebuild(): boolean;
    /**
     * Add another callback to be checked.
     */
    check(...callbacks: (() => any)[]): void;
    /**
     * Invalidate the subtree, forcing it to be redrawn.
     */
    invalidate(): void;
}