# A magic [memoization](https://en.wikipedia.org/wiki/Memoization) function
This package contains a `once` function. You can pass a `callable` to it. Here's quick example:
```php
$myClass = new class() {
public function getNumber(): int
{
return once(function () {
return rand(1, 10000);
});
}
};
```
No matter how many times you run `$myClass->getNumber()` inside the same request you'll always get the same number.
## Are you a visual learner?
Under the hood, this package uses a PHP 8 Weakmap. [In this video](https://www.youtube.com/watch?v=-lFyHJqzfFU&list=PLjzBMxW2XGTwEwWumYBaFHy1z4W32TcjU&index=13), you'll see what a weakmap is, together with a nice demo of the package.
## Support us
[](https://spatie.be/github-ad-click/once)
We invest a lot of resources into creating [best in class open source packages](https://spatie.be/open-source). You can support us by [buying one of our paid products](https://spatie.be/open-source/support-us).
We highly appreciate you sending us a postcard from your hometown, mentioning which of our package(s) you are using. You'll find our address on [our contact page](https://spatie.be/about-us). We publish all received postcards on [our virtual postcard wall](https://spatie.be/open-source/postcards).
## Installation
You can install the package via composer:
``` bash
composer require spatie/once
```
## Usage
The `once` function accepts a `callable`.
```php
$myClass = new class() {
public function getNumber(): int
{
return once(function () {
return rand(1, 10000);
});
}
};
```
No matter how many times you run `$myClass->getNumber()` you'll always get the same number.
The `once` function will only run once per combination of argument values the containing method receives.
```php
class MyClass
{
/**
* It also works in static context!
*/
public static function getNumberForLetter($letter)
{
return once(function () use ($letter) {
return $letter . rand(1, 10000000);
});
}
}
```
So calling `MyClass::getNumberForLetter('A')` will always return the same result, but calling `MyClass::getNumberForLetter('B')` will return something else.
### Flushing the cache
To flush the entire cache you can call:
```php
Spatie\Once\Cache::getInstance()->flush();
```
### Disabling the cache
In your tests you probably don't want to cache values. To disable the cache you can call:
```php
Spatie\Once\Cache::getInstance()->disable();
```
You can re-enable the cache with
```php
Spatie\Once\Cache::getInstance()->enable();
```
### Octane compatibility
> **Warning**
>
> This behaviour is in beta and needs to be tested by the community. You can find this topic [in discussion #79](https://github.com/spatie/once/discussions/79).
In order to have `once` working properly in an Octane environment, `Cache::getInstance()->flush()` must be called when `OperationTerminated` event is triggered. You can configure it in `config/octane.php` file:
```php
// config/octane.php
OperationTerminated::class => [
FlushTemporaryContainerInstances::class,
// DisconnectFromDatabases::class,
// CollectGarbage::class,
FlushSpatieOnce::class, // we should create this class we have added here
],
```
And create the `FlushSpatieOnce:class`:
```php
// app/Listeners/FlushSpatieOnce.php
use Spatie\Once\Cache;
class FlushSpatieOnce
{
public function handle($event)
{
Cache::getInstance()->flush();
}
}
```
## Under the hood
The `once` function will execute the given callable and save the result in the `$values` property of `Spatie\Once\Cache`. This class [is a singleton](https://github.com/spatie/once/blob/9decd70a76664ff451fb10f65ac360290a6a50e6/src/Cache.php#L15-L27). When we detect that `once` has already run before, we're just going to return the value stored inside [the `$values` weakmap](https://github.com/spatie/once/blob/9decd70a76664ff451fb10f65ac360290a6a50e6/src/Cache.php#L11) instead of executing the callable again.
The first thing it does is calling [`debug_backtrace`](http://php.net/manual/en/function.debug-backtrace.php). We'll use the output to determine in which function and class `once` is called and to get access to the `object` that function is running in. Yeah, we're already in voodoo-land. The output of the `debug_backtrace` is passed to a new instance of `Backtrace`. That class is just a simple wrapper, so we can work more easily with the backtrace.
```php
$trace = debug_backtrace(
DEBUG_BACKTRACE_PROVIDE_OBJECT, 2
)[1];
$backtrace = new Backtrace($trace);
$object = $backtrace->getObject();
```
Next, we calculate a `hash` of the backtrace. This hash will be unique per function `once` was called in and the values of the arguments that function receives.
```php
$hash = $backtrace->getHash();
```
Finally, we will check if there's already a value stored for the given hash. If not, then execute the given `$callback` and store the result in the weakmap of `Spatie\Once\Cache`. In the other case, we just return the value from that cache (the `$callback` isn't executed).
```php
public function has(object $object, string $backtraceHash): bool
{
if (! isset($this->values[$object])) {
return false;
}
return array_key_exists($backtraceHash, $this->values[$object]);
}
```
## Changelog
Please see [CHANGELOG](CHANGELOG.md) for more information what has changed recently.
## Testing
``` bash
composer test
```
## Contributing
Please see [CONTRIBUTING](https://github.com/spatie/.github/blob/main/CONTRIBUTING.md) for details.
## Security
If you've found a bug regarding security please mail [
[email protected]](mailto:
[email protected]) instead of using the issue tracker.
## Credits
- [Freek Van der Herten](https://github.com/freekmurze)
- [All Contributors](../../contributors)
And a special thanks to [Caneco](https://twitter.com/caneco) for the logo ✨
Credit for the idea of the `once` function goes to [Taylor Otwell](https://twitter.com/taylorotwell/status/794622206567444481). The code for this package is based upon the code he was kind enough to share with us.
## License
The MIT License (MIT). Please see [License File](LICENSE.md) for more information.