import { PullDataSource } from '@politie/sherlock';
/**
 * Lazy PullDataSource that is based on a plain javascript function that has to supply the value when someone subscribes to this
 * datasource.
 */
export declare class FunctionDataSource<T> extends PullDataSource<T> {
    private readonly fn;
    constructor(fn: () => T);
    /**
     * Required function that calculates the current value for this datasource. Will be called once everytime
     * `get()` is called when not connected. When connected, it will be called once and then only whenever `checkForChanges()`
     * was called.
     */
    calculateCurrentValue(): T;
    /**
     * Update the currently cached value of this datasource (only when connected) and notify observers when neccessary.
     */
    changed(): void;
}