Move mapReduce inline output check to a function

The MapReduce operation class will also need to call this for deciding which execute method to use in PHPLIB-316.

src/Collection.php

@@ -831,7 +831,7 @@ class Collection
      */
     public function mapReduce(JavascriptInterface $map, JavascriptInterface $reduce, $out, array $options = [])
     {
-        $hasOutputCollection = ! $this->isMapReduceOutputInline($out);
+        $hasOutputCollection = ! \MongoDB\is_mapreduce_output_inline($out);
 
         if ( ! isset($options['readPreference'])) {
             $options['readPreference'] = $this->readPreference;
@@ -984,38 +984,4 @@ class Collection
 
         return new Collection($this->manager, $this->databaseName, $this->collectionName, $options);
     }
-
-    /**
-     * Return whether the "out" option for a mapReduce operation is "inline".
-     *
-     * This is used to determine if a mapReduce command requires a primary.
-     *
-     * @see https://docs.mongodb.com/manual/reference/command/mapReduce/#output-inline
-     * @param string|array|object $out Output specification
-     * @return boolean
-     * @throws InvalidArgumentException
-     */
-    private function isMapReduceOutputInline($out)
-    {
-        if ( ! is_array($out) && ! is_object($out)) {
-            return false;
-        }
-
-        if ($out instanceof Serializable) {
-            $out = $out->bsonSerialize();
-        }
-
-        if (is_object($out)) {
-            $out = get_object_vars($out);
-        }
-
-        if ( ! is_array($out)) {
-            throw InvalidArgumentException::invalidType('$out', $out, 'array or object');
-        }
-
-        reset($out);
-        $firstKey = (string) key($out);
-
-        return $firstKey === 'inline';
-    }
 }

src/functions.php

@@ -131,6 +131,40 @@ function is_last_pipeline_operator_out(array $pipeline)
     return key($lastOp) === '$out';
 }
 
+/**
+ * Return whether the "out" option for a mapReduce operation is "inline".
+ *
+ * This is used to determine if a mapReduce command requires a primary.
+ *
+ * @internal
+ * @see https://docs.mongodb.com/manual/reference/command/mapReduce/#output-inline
+ * @param string|array|object $out Output specification
+ * @return boolean
+ * @throws InvalidArgumentException
+ */
+function is_mapreduce_output_inline($out)
+{
+    if ( ! is_array($out) && ! is_object($out)) {
+        return false;
+    }
+
+    if ($out instanceof Serializable) {
+        $out = $out->bsonSerialize();
+    }
+
+    if (is_object($out)) {
+        $out = get_object_vars($out);
+    }
+
+    if ( ! is_array($out)) {
+        throw InvalidArgumentException::invalidType('$out', $out, 'array or object');
+    }
+
+    reset($out);
+
+    return key($out) === 'inline';
+}
+
 /**
  * Converts a ReadConcern instance to a stdClass for use in a BSON document.
  *

tests/FunctionsTest.php

@@ -117,6 +117,24 @@ class FunctionsTest extends TestCase
         \MongoDB\is_first_key_operator($document);
     }
 
+    /**
+     * @dataProvider provideMapReduceOutValues
+     */
+    public function testIsMapReduceOutputInline($out, $isInline)
+    {
+        $this->assertSame($isInline, \MongoDB\is_mapreduce_output_inline($out));
+    }
+
+    public function provideMapReduceOutValues()
+    {
+        return [
+            [ 'collectionName', false ],
+            [ ['inline' => 1], true ],
+            [ ['inline' => 0], true ], // only the key is significant
+            [ ['replace' => 'collectionName'], false ],
+        ];
+    }
+
     /**
      * @dataProvider provideReadConcernsAndDocuments
      */