vendor/guzzlehttp/promises/README.md

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# Guzzle Promises

[Promises/A+](https://promisesaplus.com/) implementation that handles promise
chaining and resolution iteratively, allowing for "infinite" promise chaining
while keeping the stack size constant. Read [this blog post](https://blog.domenic.me/youre-missing-the-point-of-promises/)
for a general introduction to promises.

- [Features](#features)
- [Quick start](#quick-start)
- [Synchronous wait](#synchronous-wait)
- [Cancellation](#cancellation)
- [API](#api)
  - [Promise](#promise)
  - [FulfilledPromise](#fulfilledpromise)
  - [RejectedPromise](#rejectedpromise)
- [Promise interop](#promise-interop)
- [Implementation notes](#implementation-notes)


## Features

- [Promises/A+](https://promisesaplus.com/) implementation.
- Promise resolution and chaining is handled iteratively, allowing for
  "infinite" promise chaining.
- Promises have a synchronous `wait` method.
- Promises can be cancelled.
- Works with any object that has a `then` function.
- C# style async/await coroutine promises using
  `GuzzleHttp\Promise\Coroutine::of()`.


## Quick Start

A *promise* represents the eventual result of an asynchronous operation. The
primary way of interacting with a promise is through its `then` method, which
registers callbacks to receive either a promise's eventual value or the reason
why the promise cannot be fulfilled.

### Callbacks

Callbacks are registered with the `then` method by providing an optional 
`$onFulfilled` followed by an optional `$onRejected` function.


```php
use GuzzleHttp\Promise\Promise;

$promise = new Promise();
$promise->then(
    // $onFulfilled
    function ($value) {
        echo 'The promise was fulfilled.';
    },
    // $onRejected
    function ($reason) {
        echo 'The promise was rejected.';
    }
);
```