Merge pull request #33 from worksolutions/one-element-streaming

First element collection streaming via predicate

Author: garr1nch4

composer.json

@@ -3,7 +3,7 @@
   "description": "Collections library for php language",
   "minimum-stability": "dev",
   "license": "MIT",
-  "version": "1.0.7",
+  "version": "1.0.8",
   "authors": [
     {
       "name": "Maxim Sokolovsky",

src/WS/Utils/Collections/Functions/Predicates.php

@@ -288,4 +288,20 @@ public static function whereLessOrEqual(string $property, $value): Closure
             return ObjectFunctions::getPropertyValue($ob, $property) <= $value;
         };
     }
+
+    /**
+     * Returns <Fn($el: mixed): bool> passed only one time with first element
+     * @return Closure
+     */
+    public static function first(): Closure
+    {
+        $runOut = false;
+        return static function () use (& $runOut) {
+            if ($runOut) {
+                return false;
+            }
+            $runOut = true;
+            return true;
+        };
+    }
 }

tests/WS/Utils/Collections/PredicatesFunctionsTest.php

@@ -5,6 +5,7 @@
 
 namespace WS\Utils\Collections;
 
+use PHPUnit\Framework\MockObject\MockBuilder;
 use PHPUnit\Framework\TestCase;
 use WS\Utils\Collections\Functions\Predicates;
 use WS\Utils\Collections\UnitConstraints\CollectionIsEqual;
@@ -233,4 +234,26 @@ public function matchingValuesFiltering(): void
         ;
         $this->assertThat($filtered, CollectionIsEqual::to([1, 2]));
     }
+
+    /**
+     * @test
+     */
+    public function firstValueStreaming(): void
+    {
+        // Arrange
+        $FIRST_VALUE = 5;
+        $stream = self::toCollection($FIRST_VALUE, 6, 7)->stream();
+
+        $runningCount = 0;
+        // Act
+        $stream
+            ->filter(Predicates::first())
+            ->each(static function ($value) use ($FIRST_VALUE, & $runningCount) {
+                $runningCount++;
+                self::assertEquals($FIRST_VALUE, $value);
+            });
+
+        // Assert
+        self::assertEquals(1, $runningCount);
+    }
 }