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<?php |
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namespace Chadicus\Marvel\Api\Cache; |
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use Psr\SimpleCache\CacheInterface; |
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/** |
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* A PSR-16 implementation which does not save or store any data. |
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*/ |
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final class NullCache implements CacheInterface |
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{ |
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/** |
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* Fetches a value from the cache. |
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* |
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* @param string $key The unique key of this item in the cache. |
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* @param mixed $default Default value to return if the key does not exist. |
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* |
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* @return mixed The value of the item from the cache, or $default in case of cache miss. |
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*/ |
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public function get($key, $default = null)//@codingStandardsIgnoreLine Interface does not define type-hints |
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{ |
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return $default; |
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} |
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/** |
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* Persists data in the cache, uniquely referenced by a key with an optional expiration TTL time. |
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* |
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* @param string $key The key of the item to store. |
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* @param mixed $value The value of the item to store, must be serializable. |
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* @param null|integer|DateInterval $ttl Optional. The TTL value of this item. If no value is sent and |
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* the driver supports TTL then the library may set a default value |
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* for it or let the driver take care of that. |
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* |
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* @return boolean True on success and false on failure. |
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*/ |
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public function set($key, $value, $ttl = null)//@codingStandardsIgnoreLine Interface does not define type-hints |
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{ |
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return true; |
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} |
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/** |
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* Delete an item from the cache by its unique key. |
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* |
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* @param string $key The unique cache key of the item to delete. |
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* |
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* @return boolean True if the item was successfully removed. False if there was an error. |
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*/ |
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public function delete($key)//@codingStandardsIgnoreLine Interface does not define type-hints |
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{ |
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return true; |
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} |
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/** |
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* Wipes clean the entire cache's keys. |
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* |
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* @return boolean True on success and false on failure. |
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*/ |
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public function clear() |
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{ |
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return true; |
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} |
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/** |
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* Obtains multiple cache items by their unique keys. |
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* |
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* @param iterable $keys A list of keys that can obtained in a single operation. |
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* @param mixed $default Default value to return for keys that do not exist. |
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* |
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* @return array A list of key => value pairs. Keys that do not exist or are stale will have $default as value. |
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*/ |
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public function getMultiple($keys, $default = null)//@codingStandardsIgnoreLine Interface does not define type-hints |
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{ |
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$items = []; |
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foreach ($keys as $key) { |
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$items[$key] = $default; |
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} |
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return $items; |
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} |
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/** |
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* Persists a set of key => value pairs in the cache, with an optional TTL. |
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* |
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* @param iterable $values A list of key => value pairs for a multiple-set operation. |
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* @param null|integer|DateInterval $ttl Optional. The TTL value of this item. If no value is sent and |
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* the driver supports TTL then the library may set a default value |
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* for it or let the driver take care of that. |
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* |
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* @return boolean True on success and false on failure. |
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*/ |
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public function setMultiple($values, $ttl = null)//@codingStandardsIgnoreLine Interface does not define type-hints |
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{ |
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return true; |
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} |
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/** |
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* Deletes multiple cache items in a single operation. |
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* |
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* @param iterable $keys A list of string-based keys to be deleted. |
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* |
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* @return boolean True if the items were successfully removed. False if there was an error. |
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*/ |
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public function deleteMultiple($keys)//@codingStandardsIgnoreLine Interface does not define type-hints |
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{ |
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return true; |
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} |
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/** |
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* Determines whether an item is present in the cache. |
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* |
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* NOTE: It is recommended that has() is only to be used for cache warming type purposes |
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* and not to be used within your live applications operations for get/set, as this method |
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* is subject to a race condition where your has() will return true and immediately after, |
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* another script can remove it making the state of your app out of date. |
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* |
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* @param string $key The cache item key. |
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* |
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* @return boolean |
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*/ |
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public function has($key)//@codingStandardsIgnoreLine Interface does not define type-hints |
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{ |
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return false; |
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} |
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} |
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If you return a value from a function or method, it should be a sub-type of the type that is given by the parent type f.e. an interface, or abstract method. This is more formally defined by the Lizkov substitution principle, and guarantees that classes that depend on the parent type can use any instance of a child type interchangably. This principle also belongs to the SOLID principles for object oriented design.
Let’s take a look at an example:
Our function
my_function
expects aPost
object, and outputs the author of the post. The base classPost
returns a simple string and outputting a simple string will work just fine. However, the child classBlogPost
which is a sub-type ofPost
instead decided to return anobject
, and is therefore violating the SOLID principles. If aBlogPost
were passed tomy_function
, PHP would not complain, but ultimately fail when executing thestrtoupper
call in its body.