A magic memoization function

This package contains a once function. You can pass a callable to it. Here's quick example:

$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, you'll see what a weakmap is, together with a nice demo of the package.

Support us

We invest a lot of resources into creating best in class open source packages. You can support us by buying one of our paid products.

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. We publish all received postcards on our virtual postcard wall.

Installation

You can install the package via composer:

composer require spatie/once

Usage

The once function accepts a callable.

$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.

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:

Spatie\Once\Cache::getInstance()->flush();

Disabling the cache

In your test you probably don't want to cache values. To disable the cache you can call:

Spatie\Once\Cache::getInstance()->disable();

You can re-enable the cache with

Spatie\Once\Cache::getInstance()->enable();

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. When we detect that once has already run before, we're just going to return the value stored inside the $values weakmap instead of executing the callable again.

The first thing it does is calling debug_backtrace. 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.

$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.

$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).

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 for more information what has changed recently.

Testing

composer test

Contributing

Please see CONTRIBUTING for details.

Security

If you discover any security related issues, please email freek@spatie.be instead of using the issue tracker.

Credits

And a special thanks to Caneco for the logo ✨

Credit for the idea of the once function goes to Taylor Otwell. 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 for more information.

caneco/once