export declare function constant(x: any): () => any;
export declare function sumBy(arr: any, func: any): number;
/**
 * 计算最大值
 * @param arr
 * @param func
 */
export declare function maxValueBy(arr: any, func: any): number;
/**
 * 计算最小值
 * @param arr
 * @param func
 */
export declare function minValueBy(arr: any, func: any): number;
