introduced stop flags (refs #12817)

composer.json

@@ -14,7 +14,7 @@
         }
     },
     "autoload-dev": {
-        "psr-4": { "finc\\Rules\\": "test/" }
+        "psr-4": { "finc\\Rules\\": "tests/" }
     },
     "require-dev": {
         "phpunit/phpunit": "^5"

src/Evaluator.php

@@ -41,6 +41,7 @@ use Symfony\Component\ExpressionLanguage\ExpressionLanguage as Engine;
  */
 class Evaluator
 {
+    const STOP_FLAG = 'STOP';
     /**
      * @var Engine The engine to use for rule evaluation.
      */
@@ -51,21 +52,31 @@ class Evaluator
      */
     protected $rules;
 
+    /**
+     * @var string[] List of context variable names wich will stop further rule
+     *               evaluation when set to some truthy value.
+     */
+    protected $stopFlags;
+
     /**
      * Constructor.
      *
-     * @param array $rules List of rules to be evaluated.
+     * @param array    $rules List of rules to be evaluated.
+     * @param string[] $stopFlag
      */
-    public function __construct(array $rules = [])
+    public function __construct(array $rules, array $stopFlags = [])
     {
         $this->engine = new Engine;
         $this->rules = $rules;
+        $this->stopFlags = $stopFlags;
 
-        uksort($this->rules, function ($firstIdx, $secondIdx) {
+        uksort(
+            $this->rules, function ($firstIdx, $secondIdx) {
             $firstPrio = intval($this->rules[$firstIdx][0]);
             $secondPrio = intval($this->rules[$secondIdx][0]);
             return $secondPrio - $firstPrio ?: $secondIdx - $firstIdx;
-        });
+        }
+        );
     }
 
     /**
@@ -75,6 +86,8 @@ class Evaluator
      */
     public function __invoke(array $context = [])
     {
+        $stopFlags = array_fill_keys($this->stopFlags, false);
+        $context = array_merge($stopFlags, $context);
         return $this->evaluate($context, ...$this->rules);
     }
 
@@ -96,6 +109,10 @@ class Evaluator
             return $context;
         }
 
+        foreach ($this->stopFlags as $stopFlag) {
+            if ($context[$stopFlag]) return $context;
+        }
+
         list(, $head, $body) = $rule;
         $context[$head] = $this->engine->evaluate($body, $context);
         return $this->evaluate($context, ...$rules);

test/EvaluatorTest.php → tests/EvaluatorTest.php

@@ -43,15 +43,33 @@ class EvaluatorTest extends TestCase
 {
     protected $rules
         = [
-            [50, 'e', 'd * d'],
-            ['100', 'd', 'a.f("xyz") * 2 - 2']
+            // 5th rule
+            [80, 't', '[1]'],
+            // 4th rule
+            [85, 'e', 'e + e'],
+            // 3rd rule
+            [90, 's', '[]'],
+            // 2nd rule
+            [95, 'e', '1'],
+            // 1st rule
+            ['100', 'd', 'a.f("xyz") * 2 - 2'],
+            // last rule due to lowest priority
+            [75, 'e', 'd * d'],
         ];
 
-    public function test()
+    public function testSimple()
     {
         $evaluator = new Evaluator($this->rules);
         $initialContext = ['a' => new ContextObject, 'b' => 3];
         $resultContext = $evaluator($initialContext);
         $this->assertArraySubset(['d' => 4, 'e' => 16], $resultContext);
     }
+
+    public function testStop()
+    {
+        $evaluator = new Evaluator($this->rules, ['s', 't']);
+        $initialContext = ['a' => new ContextObject, 'b' => 3];
+        $resultContext = $evaluator($initialContext);
+        $this->assertArraySubset(['d' => 4, 'e' => 2], $resultContext);
+    }
 }