///
module Rx {
export interface Observable {
/**
* Returns elements from an observable sequence as long as a specified condition is true.
* The element's index is used in the logic of the predicate function.
* @param {Function} predicate A function to test each element for a condition; the second parameter of the function represents the index of the source element.
* @param {Any} [thisArg] Object to use as this when executing callback.
* @returns {Observable} An observable sequence that contains the elements from the input sequence that occur before the element at which the test no longer passes.
*/
takeWhile(predicate: _Predicate, thisArg?: any): Observable;
}
}