The once() Memoization Helper is Coming to Laravel 11

The once() function was originally inspired by this tweet by Taylor Otwell, made into a package by Spatie, and now finds its way into the core of Laravel framework in Laravel 11.

This helper ensures that you'll always get the same value no matter how many times you call an object method. The once function is helpful when you have some code that you want to ensure only ever runs one time.

Let’s use the new Laravel 11 make:class Artisan command to demonstrate how it works:

php artisan make:class OnceDemo

Here’s the OnceDemo code that demonstrates how memoization works:

<?php
 
namespace App;
 
use Illuminate\Support\Str;
use Ramsey\Uuid\UuidInterface;
 
class OnceDemo
{
    public function uuid(): UuidInterface
    {
        return Str::uuid();
    }
 
    public function uuidOnce(): UuidInterface
    {
        return once(fn (): UuidInterface => $this->uuid());
    }
}

If you run the following PHP code without using the once() helper, you’ll get a new UUID with each method call:

$demo = new App\OnceDemo;
 
foreach (range(1,5) as $_) {
    echo $demo->uuid() . "\n";
}
 
/*
9ee5dc3c-f34b-4424-827d-13b662bb0ce1
ad9cca9d-4e98-4307-994c-c610df7c70ac
d642bc9e-d8bb-4bfe-a647-78b555b22e1c
7968b5f2-80f4-40de-95e0-e1f576c37e60
78b69cbb-07b3-45a4-b77b-edefb16f2782
*/

However, if you run the same code using the once() helper, you’ll get the same result each time:

$demo = new App\OnceDemo;
 
foreach (range(1,5) as $_) {
    echo $demo->uuidOnce() . "\n";
}
 
/*
5cdfa44b-5ae5-4b0f-8a6f-4b167307fa05
5cdfa44b-5ae5-4b0f-8a6f-4b167307fa05
5cdfa44b-5ae5-4b0f-8a6f-4b167307fa05
5cdfa44b-5ae5-4b0f-8a6f-4b167307fa05
5cdfa44b-5ae5-4b0f-8a6f-4b167307fa05
*/

This method will always return the same object instance in our demo example, and you can verify this behavior:

$demo = new App\OnceDemo;
 
foreach (range(1,5) as $_) {
    echo spl_object_id($demo->uuidOnce()) . "\n";
}
 
/*
5075
5075
5075
5075
5075
*/

When running tests, the memoization function must be cleared after each test to ensure you are working in a pristine state. Laravel takes care of this detail for you in the base TestCase class using the Once::flush(); method.

Shout out to Nuno Maduro, who implemented this feature in Pull Request #49744!