add methods set and unset

spec/IW/ServiceContainerSpec.php

@@ -88,6 +88,23 @@ function it_provides_aliased_service() {
         $this->get(Service::class)->shouldBeAnInstanceOf(Service::class);
     }
 
+    function it_can_be_injected_with_given_instance() {
+        $now = new \DateTime;
+        $this->set('now', $now);
+        $this->get('now')->shouldBe($now);
+    }
+
+    function it_can_be_injected_with_given_anything() {
+        $this->set('fb', ['foo' => 'bar']);
+        $this->get('fb')->shouldBe(['foo' => 'bar']);
+    }
+
+    function it_can_forget_injected_singleton() {
+        $this->set('fb', ['foo' => 'bar']);
+        $this->unset('fb');
+        $this->has('fb')->shouldReturn(false);
+    }
+
 }
 
 class Foo {}

src/ServiceContainer.php

@@ -147,13 +147,26 @@ public function bind(string $id, callable $factory): void
         $this->factories[$id] = $factory;
     }
 
+    /**
+     * Sets given entry as a singleton
+     *
+     * @param string $id    ID of entry
+     * @param mixed  $entry actual entry
+     *
+     * @return void
+     */
+    public function set(string $id, $entry): void
+    {
+        $this->instances[$id] = $entry;
+    }
+
     /**
      * Mark particular ID to be a singleton, this is useful when global singletons
      * are disabled but you still few.
      *
      * Note in good design you should not need much singletons
      *
-     * @param string $id ID of singleton
+     * @param string $id ID of singleton to set
      *
      * @return void
      */
@@ -162,6 +175,22 @@ public function singleton(string $id): void
         $this->instances[$id] = $this->get($id);
     }
 
+    /**
+     * Unset a singleton with given ID, returns TRUE if singleton was set, FALSE otherwise
+     *
+     * @param string $id ID of singleton to unset
+     *
+     * @return bool
+     */
+    public function unset(string $id): bool {
+        if (array_key_exists($id, $this->instances)) {
+            unset($this->instances[$id]);
+            return true;
+        }
+
+        return false;
+    }
+
     private static function buildFactory($classname)
     {
         try {