<?php 
namespace GuzzleHttp\Promise; 
 
/** 
 * 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. 
 * 
 * @link https://promisesaplus.com/ 
 */ 
interface PromiseInterface 
{ 
    const PENDING = 'pending'; 
    const FULFILLED = 'fulfilled'; 
    const REJECTED = 'rejected'; 
 
    /** 
     * Appends fulfillment and rejection handlers to the promise, and returns 
     * a new promise resolving to the return value of the called handler. 
     * 
     * @param callable $onFulfilled Invoked when the promise fulfills. 
     * @param callable $onRejected  Invoked when the promise is rejected. 
     * 
     * @return PromiseInterface 
     */ 
    public function then( 
        callable $onFulfilled = null, 
        callable $onRejected = null 
    ); 
 
    /** 
     * Appends a rejection handler callback to the promise, and returns a new 
     * promise resolving to the return value of the callback if it is called, 
     * or to its original fulfillment value if the promise is instead 
     * fulfilled. 
     * 
     * @param callable $onRejected Invoked when the promise is rejected. 
     * 
     * @return PromiseInterface 
     */ 
    public function otherwise(callable $onRejected); 
 
    /** 
     * Get the state of the promise ("pending", "rejected", or "fulfilled"). 
     * 
     * The three states can be checked against the constants defined on 
     * PromiseInterface: PENDING, FULFILLED, and REJECTED. 
     * 
     * @return string 
     */ 
    public function getState(); 
 
    /** 
     * Resolve the promise with the given value. 
     * 
     * @param mixed $value 
     * @throws \RuntimeException if the promise is already resolved. 
     */ 
    public function resolve($value); 
 
    /** 
     * Reject the promise with the given reason. 
     * 
     * @param mixed $reason 
     * @throws \RuntimeException if the promise is already resolved. 
     */ 
    public function reject($reason); 
 
    /** 
     * Cancels the promise if possible. 
     * 
     * @link https://github.com/promises-aplus/cancellation-spec/issues/7 
     */ 
    public function cancel(); 
 
    /** 
     * Waits until the promise completes if possible. 
     * 
     * Pass $unwrap as true to unwrap the result of the promise, either 
     * returning the resolved value or throwing the rejected exception. 
     * 
     * If the promise cannot be waited on, then the promise will be rejected. 
     * 
     * @param bool $unwrap 
     * 
     * @return mixed 
     * @throws \LogicException if the promise has no wait function or if the 
     *                         promise does not settle after waiting. 
     */ 
    public function wait($unwrap = true); 
} 
 
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