Fixed some warnings

Author: byjg

src/Engine/FileSystemCacheEngine.php

@@ -100,7 +100,8 @@ public function set($key, $object, $ttl = 0)
                 file_put_contents($fileKey, serialize($object));
             }
         } catch (Exception $ex) {
-            echo "<br/><b>Warning:</b> I could not write to cache on file '" . basename($key) . "'. Switching to nocache=true mode. <br/>";
+            $this->logger->warning("[Filesystem cache] I could not write to cache on file '" . basename($key) . "'. Switching to nocache=true mode.");
+            return false;
         }
 
         return true;
@@ -130,8 +131,11 @@ public function append($key, $content, $ttl = 0)
         try {
             file_put_contents($fileKey, serialize($content), true);
         } catch (Exception $ex) {
-            echo "<br/><b>Warning:</b> I could not write to cache on file '" . basename($key) . "'. Switching to nocache=true mode. <br/>";
+            $this->logger->warning("[Filesystem cache] I could not write to cache on file '" . basename($key) . "'. Switching to nocache=true mode.");
+            return false;
         }
+
+        return true;
     }
 
     /**

src/Engine/RedisCacheEngine.php

@@ -3,7 +3,6 @@
 namespace ByJG\Cache\Engine;
 
 use ByJG\Cache\CacheEngineInterface;
-use Memcached;
 use Psr\Log\NullLogger;
 
 class RedisCacheEngine implements CacheEngineInterface

src/Engine/ShmopCacheEngine.php

@@ -125,8 +125,6 @@ public function get($key, $ttl = 0)
      */
     public function set($key, $object, $ttl = 0)
     {
-        
-
         $this->logger->info("[Shmop Cache] set '$key'");
 
         $this->release($key);
@@ -155,6 +153,8 @@ public function set($key, $object, $ttl = 0)
             $this->logger->warning("Couldn't write the entire length of data");
         }
         shmop_close($shm_id);
+
+        return true;
     }
 
     /**
@@ -178,6 +178,8 @@ public function append($key, $str)
                 throw new InvalidArgumentException('Only is possible append string types');
             }
         }
+
+        return true;
     }
 
     /**

src/Psr/CachePool.php

@@ -170,7 +170,7 @@ public function clear()
      * Psr implementation of deleteItem()
      *
      * @param string $key
-     * @return bool|void
+     * @return bool
      */
     public function deleteItem($key)
     {
@@ -181,7 +181,7 @@ public function deleteItem($key)
      * Psr Implementation of deleteItems()
      * 
      * @param array $keys
-     * @return bool|void
+     * @return bool
      */
     public function deleteItems(array $keys)
     {
@@ -195,7 +195,7 @@ public function deleteItems(array $keys)
 
     /**
      * @param CacheItemInterface $item
-     * @return bool|void
+     * @return bool
      */
     public function save(CacheItemInterface $item)
     {
@@ -222,7 +222,7 @@ public function save(CacheItemInterface $item)
      * Psr Implementation of saveDeferred()
      * 
      * @param CacheItemInterface $item
-     * @return bool|void
+     * @return bool
      */
     public function saveDeferred(CacheItemInterface $item)
     {