As an example, if we wanted to replicate the latestPosts query method in our PostRepository by using a Specification for an in-memory implementation, it would look like this:

namespace InfrastructurePersistenceInMemory;

use DomainModelPost;

interface InMemoryPostSpecification
{
    /**
     * @return boolean
     */
     public function specifies(Post $aPost);
}

The in-memory implementation for the latestPosts behavior could look like this:

namespace InfrastructurePersistenceInMemory;
use DomainModelPost;

class InMemoryLatestPostSpecification
    implements InMemoryPostSpecification
{
    private $since;

    public function __construct(DateTimeImmutable $since)
    {
       $this->since = $since;
    }

    public function specifies(Post $aPost)
    {
      return $aPost->createdAt() > $this->since;
    }
}

The query method for our Repository implementation could look like this:

class InMemoryPostRepository implements PostRepository
{
    // ...

    /**
     * @param InMemoryPostSpecification $specification
     *
     * @return Post[]
     */
    public function query($specification)
    {
        return $this->filterPosts(
            function (Post $post) use($specification) {
                return $specification->specifies($post);
            }
        );
    }
}

Retrieving all the latest posts from the Repository is as simple as creating a tailored instance of the above implementation:

$latestPosts = $postRepository->query(
    new InMemoryLatestPostSpecification(new DateTimeImmutable('-24'))
);