Add is(Not)Empty helper methods

README.adoc

@@ -169,6 +169,25 @@ $brief->a_rose === $brief->montague;
 // true
 ----
 
+=== Custom Empty Test
+
+Brief comes with `isEmpty()` and `isNotEmpty()` which somewhat naively test if the Brief is empty
+(they examine only whether top-level items in the array are not equal to `null`).
+If your use case requires a more robust test, you can pass that test to the `isEmpty` parameter at instantiation.
+It accepts anything PHP considers callable.
+
+[source,php]
+----
+$brief = Brief::make([
+    ['key' => 'value'],
+    ['isEmpty' => function($brief) {
+        // some logic
+    }]
+);
+
+$brief->isEmpty(); // false (hopefully)
+----
+
 === Logging
 
 Since the basic concept for Brief is about how either your data exists or doesn't, Brief will not complain loudly if you do something it doesn't like.

src/Brief.php

@@ -141,6 +141,9 @@ public function parseSettings(array $settings)
                 case 'logger':
                     $this->setUpLogger($arg);
                     break;
+                case 'isEmpty':
+                    $this->setUpIsEmpty($arg);
+                    break;
             }
         }
     }
@@ -169,6 +172,20 @@ protected function setUpLogger($callable)
         }
     }
 
+    /**
+     * Attach isEmpty text to Brief, if valid.
+     *
+     * This callable will be passed a copy of the Brief to evaluate.
+     *
+     * @param $callable
+     */
+    protected function setUpIsEmpty($callable)
+    {
+        if (is_callable($callable)) {
+            $this->callables['isEmpty'] = $callable;
+        }
+    }
+
     /**
      * Store multiple values, as defined by an array.
      *
@@ -839,4 +856,38 @@ public function transform(callable $callable)
 
         return $this;
     }
+
+    /**
+     * Determines whether the Brief is empty.
+     *
+     * The default test is somewhat naive, but you can pass your own test via
+     * the `isEmpty` setting on instantiation.
+     *
+     * @return bool|mixed
+     */
+    public function isEmpty()
+    {
+        $Clone = clone $this;
+
+        if (isset($this->callables['isEmpty']) && is_callable($this->callables['isEmpty'])) {
+            $result = call_user_func($this->callables['isEmpty'], $Clone);
+            unset($Clone);
+
+            return $result;
+        }
+
+        return count(array_filter(array_column($this->store, 'value'), function ($value) {
+                return $value !== null;
+            })) < 1;
+    }
+
+    /**
+     * If the Brief is *not* empty.
+     *
+     * @return bool
+     */
+    public function isNotEmpty()
+    {
+        return !$this->isEmpty();
+    }
 }

tests/BriefTest.php

@@ -447,6 +447,39 @@ public function testSetKeyAndValueDynamically(): void
         $this->assertEquals('new value', $Brief->new_key);
         $this->assertNotEquals('new value', $Brief->any_key);
     }
+
+    public function testCanDetermineEmptyBriefs(): void
+    {
+        $Brief = Brief::make([]);
+        $this->assertTrue($Brief->isEmpty());
+        $this->assertFalse($Brief->isNotEmpty());
+
+        $SortOfEmpty = Brief::make([
+            'key' => null,
+        ]);
+        $this->assertTrue($SortOfEmpty->isEmpty());
+        $this->assertFalse($SortOfEmpty->isNotEmpty());
+
+        $NotActuallyEmpty = Brief::make([
+            'key' => false,
+        ]);
+        $this->assertFalse($NotActuallyEmpty->isEmpty());
+        $this->assertTrue($NotActuallyEmpty->isNotEmpty());
+    }
+
+    public function testCanUserCustomEmptyFunction(): void
+    {
+        $test = function(Brief $brief) {
+            return count(array_filter($brief->getKeyed())) < 1;
+        };
+        $Brief = Brief::make([], ['isEmpty' => $test]);
+        $this->assertTrue($Brief->isEmpty());
+
+        $Brieful = Brief::make([
+            'key' => 'value',
+        ], ['isEmpty' => $test]);
+        $this->assertFalse($Brieful->isEmpty());
+    }
 }
 
 /**