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<?php declare (strict_types=1);
namespace Sabre\Event;
use Generator;
use Throwable;
/**
* Turn asynchronous promise-based code into something that looks synchronous
* again, through the use of generators.
*
* Example without coroutines:
*
* $promise = $httpClient->request('GET', '/foo');
* $promise->then(function($value) {
*
* return $httpClient->request('DELETE','/foo');
*
* })->then(function($value) {
*
* return $httpClient->request('PUT', '/foo');
*
* })->error(function($reason) {
*
* echo "Failed because: $reason\n";
*
* });
*
* Example with coroutines:
*
* coroutine(function() {
*
* try {
* yield $httpClient->request('GET', '/foo');
* yield $httpClient->request('DELETE', /foo');
* yield $httpClient->request('PUT', '/foo');
* } catch(\Throwable $reason) {
* echo "Failed because: $reason\n";
* }
*
* });
*
* @return \Sabre\Event\Promise
* @copyright Copyright (C) fruux GmbH (https://fruux.com/)
* @author Evert Pot (http://evertpot.com/)
* @license http://sabre.io/license/ Modified BSD License
*/
function coroutine(callable $gen) : Promise {
$generator = $gen();
if (!$generator instanceof Generator) {
throw new \InvalidArgumentException('You must pass a generator function');
}
// This is the value we're returning.
$promise = new Promise();
/**
* So tempted to use the mythical y-combinator here, but it's not needed in
* PHP.
*/
$advanceGenerator = function() use (&$advanceGenerator, $generator, $promise, &$lastYieldResult) {
while ($generator->valid()) {
$yieldedValue = $generator->current();
if ($yieldedValue instanceof Promise) {
$yieldedValue->then(
function($value) use ($generator, &$advanceGenerator, &$lastYieldResult) {
$generator->send($value);
$advanceGenerator();
},
function(Throwable $reason) use ($generator, $advanceGenerator) {
$generator->throw($reason);
$advanceGenerator();
}
)->otherwise(function(Throwable $reason) use ($promise) {
// This error handler would be called, if something in the
// generator throws an exception, and it's not caught
// locally.
$promise->reject($reason);
});
// We need to break out of the loop, because $advanceGenerator
// will be called asynchronously when the promise has a result.
break;
} else {
// If the value was not a promise, we'll just let it pass through.
$generator->send($yieldedValue);
}
}
// If the generator is at the end, and we didn't run into an exception,
// We're grabbing the "return" value and fulfilling our top-level
// promise with its value.
if (!$generator->valid() && $promise->state === Promise::PENDING) {
$returnValue = $generator->getReturn();
// The return value is a promise.
if ($returnValue instanceof Promise) {
$returnValue->then(function($value) use ($promise) {
$promise->fulfill($value);
}, function(Throwable $reason) {
$promise->reject($reason);
});
} else {
$promise->fulfill($returnValue);
}
}
};
try {
$advanceGenerator();
} catch (Throwable $e) {
$promise->reject($e);
}
return $promise;
}
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