[Feature request] Add class cache syntax

[Nuranto]

Description

It happens a lot to use class property as a caching method.

For example :

class OrderStatus {
      protected $statusLabels = [];

      public function getStatusLabel(int $statusCode) {
              if(!isset($this->statusLabels[$statusCode])) {
                      $this->statusLabels[$statusCode] = $this->loadStatusLabelFromDatabase($statusCode);
              }
              return $this->statusLabels[$statusCode];
      }
}

Would be great to have some new syntax to do this behind the scene :

class OrderStatus {
      public cacheable function getStatusLabel(int $statusCode) {
              return $this->loadStatusLabelFromDatabase($statusCode);
      }
}

Of course, some rules should exists, like a function cannot be cached if some parameters are not typed or not a basic type, or dynamic, since this feature requires to serialize method parameters.

What do you think ?

[KapitanOczywisty]

Would this work across requests, object instances or only single instance? How cache would be limited to not starve memory?

[iluuu1994]

It might make more sense to have something akin to Swift's lazy properties that can actually be reset. Putting this on a method would require more syntax or reflection just to delete the cache.

[ju1ius]

As @KapitanOczywisty mentioned, caching is a complex topic that should be handled by the application, not the language.

If you want a per-instance in-memory cache, use a private property.
If you want an in-memory cache bound to the lifetime of a single request, use a static property.
Anything else, pass a cache service to your instance constructor.

And for some syntactic sugar, you can use ??=, AKA the almighty null-coalescing assignment operator:

final class OrderStatus {
  private static array $labels = [];
  public function getStatusLabel(int $statusCode): string {
    return self::$labels[$statusCode] ??= $this->loadStatusLabel($statusCode);
  }
  private function loadStatusLabel(int $statusCode): string {
    return "Status: {$statusCode}";
  }
}

[cmb69]

The keyword here would be memoization, by the way.