Add $default to return instead of null on cache miss for get()

README.md

@@ -37,6 +37,12 @@ provide alternate implementations.
 
 #### get()
 
+The `get(string $key, mixed $default = null): PromiseInterfae` method can be used to
+retrieve an item from the cache.
+
+This method will resolve with the cached value on success or with the
+given `$default` value when no item can be found or when an error occurs.
+
 ```php
 $cache
  ->get('foo')
@@ -47,9 +53,6 @@ This example fetches the value of the key `foo` and passes it to the
 `var_dump` function. You can use any of the composition provided by
 [promises](https://github.com/reactphp/promise).
 
-If the key `foo` does not exist, the promise will be fulfilled with `null` as value. On 
-any error it will also resolve with `null`.
-
 #### set()
 
 ```php

src/ArrayCache.php

@@ -41,10 +41,10 @@ public function __construct($limit = null)
  $this->limit = $limit;
  }
 
- public function get($key)
+ public function get($key, $default = null)
 {
- if (!isset($this->data[$key])){
- return Promise\resolve();
+ if (!array_key_exists($key, $this->data)){
+ return Promise\resolve($default);
  }
 
  // remove and append to end of array to keep track of LRU info

src/CacheInterface.php

@@ -7,13 +7,26 @@
 interface CacheInterface
 {
  /**
- * Retrieve an item from the cache, resolves with its value on
- * success or null when no item can be found or when an error occurs.
+ * Retrieves an item from the cache.
+ *
+ * This method will resolve with the cached value on success or with the
+ * given `$default` value when no item can be found or when an error occurs.
+ *
+ * ```php
+ * $cache
+ * ->get('foo')
+ * ->then('var_dump');
+ * ```
+ *
+ * This example fetches the value of the key `foo` and passes it to the
+ * `var_dump` function. You can use any of the composition provided by
+ * [promises](https://github.com/reactphp/promise).
  *
  * @param string $key
+ * @param mixed $default Default value to return for cache miss or null if not given.
  * @return PromiseInterface
  */
- public function get($key);
+ public function get($key, $default = null);
 
  /**
  * Store an item in the cache, returns a promise which resolves to true on success or

tests/ArrayCacheTest.php

@@ -83,6 +83,28 @@ public function removeShouldRemoveKey()
  );
  }
 
+ public function testGetWillResolveWithNullForCacheMiss()
+{
+ $this->cache = new ArrayCache();
+
+ $this->cache->get('foo')->then($this->expectCallableOnceWith(null));
+ }
+
+ public function testGetWillResolveWithDefaultValueForCacheMiss()
+{
+ $this->cache = new ArrayCache();
+
+ $this->cache->get('foo', 'bar')->then($this->expectCallableOnceWith('bar'));
+ }
+
+ public function testGetWillResolveWithExplicitNullValueForCacheHit()
+{
+ $this->cache = new ArrayCache();
+
+ $this->cache->set('foo', null);
+ $this->cache->get('foo', 'bar')->then($this->expectCallableOnceWith(null));
+ }
+
  public function testLimitSizeToZeroDoesNotStoreAnyData()
 {
  $this->cache = new ArrayCache(0);