Add methods and tests that providing the ability to clear/delete placeholder containers

Author: gsteel

doc/book/helpers/placeholder.md

@@ -63,7 +63,7 @@ $this->placeholder('foo')
 <?= $this->placeholder('foo') ?>
 ```
 
-The above results in an unodered list with pretty indentation.
+The above results in an unordered list with pretty indentation.
 
 Because the `Placeholder` container objects extend `ArrayObject`, you can also
 assign content to a specific key in the container easily, instead of simply
@@ -131,6 +131,21 @@ foreach ($this->data as $datum): ?>
 <?= $this->placeholder('foo')->data ?>
 ```
 
+## Clearing Content
+
+In certain situations it is desirable to remove or clear containers and aggregated content. The placeholder view helper
+provides two methods to either delete a specific container or clear all containers at once:
+
+```php
+<?php
+// Delete a single Container
+$placeholderHelper = $this->plugin('placeholder');
+$placeholderHelper->deleteContainer('myNamedContainer');
+// Clear all containers at once
+$placeholderHelper->clearContainers();
+?>
+```
+
 ## Concrete Implementations
 
 zend-view ships with a number of "concrete" placeholder implementations. These

src/Helper/Placeholder.php

@@ -23,7 +23,7 @@ class Placeholder extends AbstractHelper
     /**
      * Placeholder items
      *
-     * @var array
+     * @var Container\AbstractContainer[]
      */
     protected $items = [];
 
@@ -97,4 +97,28 @@ public function containerExists($key)
         $return = array_key_exists($key, $this->items);
         return $return;
     }
+
+    /**
+     * Delete a specific container by name
+     *
+     * @param string $key
+     * @return self
+     */
+    public function deleteContainer($key)
+    {
+        $key = (string) $key;
+        unset($this->items[$key]);
+        return $this;
+    }
+
+    /**
+     * Remove all containers
+     *
+     * @return self
+     */
+    public function clearContainers()
+    {
+        $this->items = [];
+        return $this;
+    }
 }

test/Helper/PlaceholderTest.php

@@ -77,4 +77,29 @@ public function testPlaceholderRetrievesSameContainerOnSubsequentCalls()
         $container2 = $this->placeholder->__invoke('foo');
         $this->assertSame($container1, $container2);
     }
+
+    public function testContainersCanBeDeleted()
+    {
+        $container = $this->placeholder->__invoke('foo');
+        $container->set('Value');
+        $this->assertTrue($this->placeholder->containerExists('foo'));
+        $this->assertSame('Value', (string) $this->placeholder->__invoke('foo'));
+        $this->placeholder->deleteContainer('foo');
+        $this->assertFalse($this->placeholder->containerExists('foo'));
+        $this->assertSame('', (string) $this->placeholder->__invoke('foo'));
+    }
+
+    public function testClearContainersRemovesAllContainers()
+    {
+        $this->placeholder->__invoke('foo');
+        $this->placeholder->__invoke('bar');
+
+        $this->assertTrue($this->placeholder->containerExists('foo'));
+        $this->assertTrue($this->placeholder->containerExists('bar'));
+
+        $this->placeholder->clearContainers();
+
+        $this->assertFalse($this->placeholder->containerExists('foo'));
+        $this->assertFalse($this->placeholder->containerExists('bar'));
+    }
 }