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<?php |
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/** |
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* Src/Cache/Cache.php |
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* |
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* @package Ds\Cache |
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* @subpackage Cache |
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* @author Dan Smith <[email protected]> |
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* @version v.1 (20/03/2017) |
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* @copyright Copyright (c) 2017, Dan Smith |
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*/ |
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namespace Ds\Cache; |
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use Psr\SimpleCache\CacheInterface as SimpleCache; |
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use Psr\SimpleCache\DateInterval; |
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/** |
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* PSR 16 Simple Cache Component |
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* |
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* @package Ds\Cache |
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*/ |
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class Cache extends AbstractCache implements SimpleCache |
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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|int|\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 bool True on success and false on failure. |
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* |
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* @throws \Psr\SimpleCache\InvalidArgumentException |
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* MUST be thrown if the $key string is not a legal value. |
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*/ |
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public function set($key, $value, $ttl = null) |
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{ |
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//convert to timestamp from now. |
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if ($ttl instanceof \DateInterval){ |
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$dateTime = new \DateTime(); |
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$dateTime->add( $ttl ); |
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$ttl = $dateTime->getTimestamp() - time(); |
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} |
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if (!is_int($ttl) || $ttl === null){ |
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throw new InvalidArgumentException('$ttl can only be an instance of \DateInterval, int or null'); |
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} |
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return $this->cache->set($key, $value, $ttl); |
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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 bool |
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* |
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* @throws \Psr\SimpleCache\InvalidArgumentException |
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* MUST be thrown if the $key string is not a legal value. |
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*/ |
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public function has($key) |
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{ |
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$this->_isValidKey($key); |
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return $this->cache->has($key); |
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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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* @throws \Psr\SimpleCache\InvalidArgumentException |
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* MUST be thrown if the $key string is not a legal value. |
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*/ |
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public function get($key, $default = null) |
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{ |
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$this->_isValidKey($key); |
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if ($this->cache->has($key)){ |
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return $this->cache->get($key); |
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} |
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return $default; |
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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 bool True if the item was successfully removed. False if there was an error. |
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* |
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* @throws \Psr\SimpleCache\InvalidArgumentException |
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* MUST be thrown if the $key string is not a legal value. |
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*/ |
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public function delete($key) |
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{ |
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$this->_isValidKey($key); |
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return $this->cache->delete($key); |
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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 \iterable A list of key => value pairs. Cache keys that do not exist or are stale will have $default as value. |
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* |
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* @throws \Psr\SimpleCache\InvalidArgumentException |
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* MUST be thrown if $keys is neither an array nor a Traversable, |
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* or if any of the $keys are not a legal value. |
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*/ |
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public function getMultiple($keys, $default = null) |
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{ |
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$this->_isTraversable($keys); |
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$result = []; |
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foreach ((array)$keys as $key){ |
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$cachedItem = $this->cache->get($key); |
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$result[$key] = (null !== $cachedItem) ? $cachedItem : $default; |
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} |
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return (array)$result; |
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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|int|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 bool True on success and false on failure. |
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* |
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* @throws \Psr\SimpleCache\InvalidArgumentException |
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* MUST be thrown if $values is neither an array nor a Traversable, |
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* or if any of the $values are not a legal value. |
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*/ |
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public function setMultiple($values, $ttl = null) |
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{ |
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$this->_hasKeys($values); |
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$this->_isTraversable($values); |
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$results = []; |
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foreach ((array)$values as $key => $value){ |
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$results[] = $this->cache->set($key, $value, $ttl); |
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} |
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if ($this->_hasFailure($results)){ |
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return false; |
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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 bool True if the items were successfully removed. False if there was an error. |
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* |
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* @throws \Psr\SimpleCache\InvalidArgumentException |
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* MUST be thrown if $keys is neither an array nor a Traversable, |
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* or if any of the $keys are not a legal value. |
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*/ |
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public function deleteMultiple($keys) |
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{ |
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$this->_isTraversable($keys); |
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$results = []; |
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foreach ((array)$keys as $key){ |
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$results[] = $this->cache->delete($key); |
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} |
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if ($this->_hasFailure($results)){ |
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return false; |
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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 bool 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 $this->cache->clear(); |
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} |
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/** |
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* Check that provided key is valid. |
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* |
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* @param $key |
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* @throws InvalidArgumentException |
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*/ |
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private function _isValidKey($key){ |
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if (!is_string($key)){ |
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throw new InvalidArgumentException('provided key must be a valid string'); |
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} |
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} |
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/** |
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* Check that $keys are traversable |
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* |
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* @param $data |
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* @throws InvalidArgumentException |
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* @return bool |
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* @internal |
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*/ |
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private function _isTraversable($data){ |
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if (is_array($data) || $data instanceof \Traversable){ |
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return true; |
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} |
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throw new InvalidArgumentException('Keys must be traversable'); |
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} |
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/** |
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* @param array $arr |
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* @return bool |
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* @throws InvalidArgumentException |
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*/ |
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private function _hasKeys(array $arr) |
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{ |
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if (array() === $arr || array_keys($arr) === range(0, count($arr) - 1)){ |
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throw new InvalidArgumentException('Keys missing'); |
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} |
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return true; |
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} |
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/** |
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* Check for failures when adding multiple entries. |
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* |
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* @param array $results |
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* @return bool |
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* @internal |
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*/ |
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private function _hasFailure(array $results){ |
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if (in_array(false, $results)){ |
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return true; |
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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.