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amp/lib/LazyPromise.php
2020-09-26 22:26:57 -05:00

45 lines
1.2 KiB
PHP

<?php
namespace Amp;
/**
* Creates a promise that calls $promisor only when the result of the promise is requested (i.e. onResolve() is called
* on the promise). $promisor can return a promise or any value. If $promisor throws an exception, the promise fails
* with that exception. If $promisor returns a Generator, it will be run as a coroutine.
*/
final class LazyPromise implements Promise
{
/** @var callable|null */
private $promisor;
/** @var Promise|null */
private ?Promise $promise;
/**
* @param callable $promisor Function which starts an async operation, returning a Promise (or any value).
* Generators will be run as a coroutine.
*/
public function __construct(callable $promisor)
{
$this->promisor = $promisor;
}
/**
* @inheritDoc
*/
public function onResolve(callable $onResolved): void
{
if (!isset($this->promise)) {
\assert($this->promisor !== null);
$provider = $this->promisor;
$this->promisor = null;
$this->promise = async(static fn (): Promise => call($provider));
}
\assert($this->promise !== null);
$this->promise->onResolve($onResolved);
}
}