import { NgForOf } from '@angular/common';
import { OnChanges, SimpleChanges, ViewContainerRef } from '@angular/core';
export declare class NgForTrackByKeyDirective<T> implements OnChanges {
    private ngFor;
    private viewContainerRef;
    ngForTrackByKey: keyof T;
    constructor(ngFor: NgForOf<T>, viewContainerRef: ViewContainerRef);
    ngOnChanges(changes: SimpleChanges): void;
}