<?php

namespace React\Promise;

interface PromiseInterface
{
/**
* Transforms a promise's value by applying a function to the promise's fulfillment
* or rejection value. Returns a new promise for the transformed result.
*
* The `then()` method registers new fulfilled and rejection handlers with a promise
* (all parameters are optional):
*
* * `$onFulfilled` will be invoked once the promise is fulfilled and passed
* the result as the first argument.
* * `$onRejected` will be invoked once the promise is rejected and passed the
* reason as the first argument.
* * `$onProgress` (deprecated) will be invoked whenever the producer of the promise
* triggers progress notifications and passed a single argument (whatever it
* wants) to indicate progress.
*
* It returns a new promise that will fulfill with the return value of either
* `$onFulfilled` or `$onRejected`, whichever is called, or will reject with
* the thrown exception if either throws.
*
* A promise makes the following guarantees about handlers registered in
* the same call to `then()`:
*
* 1. Only one of `$onFulfilled` or `$onRejected` will be called,
* never both.
* 2. `$onFulfilled` and `$onRejected` will never be called more
* than once.
* 3. `$onProgress` (deprecated) may be called multiple times.
*
* @param callable|null $onFulfilled
* @param callable|null $onRejected
* @param callable|null $onProgress This argument is deprecated and should not be used anymore.
* @return PromiseInterface
*/
public function then(callable $onFulfilled = null, callable $onRejected = null, callable $onProgress = null);
}