fix(set): map uniqueness

src/AbstractCollection.php

@@ -54,6 +54,11 @@ abstract class AbstractCollection extends AbstractArray implements CollectionInt
     use ValueToStringTrait;
     use ValueExtractorTrait;
 
+    /**
+     * @var class-string<CollectionInterface<T>>
+     */
+    protected string $collection = Collection::class;
+
     /**
      * @throws InvalidArgumentException if $element is of the wrong type.
      */
@@ -213,7 +218,8 @@ public function where(?string $propertyOrMethod, mixed $value): CollectionInterf
      */
     public function map(callable $callback): CollectionInterface
     {
-        return new Collection('mixed', array_map($callback, $this->data));
+        /** @var CollectionInterface<TCallbackReturn> */
+        return new $this->collection('mixed', array_map($callback, $this->data));
     }
 
     /**

src/Collection.php

@@ -75,6 +75,11 @@
  */
 class Collection extends AbstractCollection
 {
+    /**
+     * @psalm-suppress NonInvariantDocblockPropertyType
+     */
+    protected string $collection = self::class;
+
     /**
      * Constructs a collection object of the specified type, optionally with the
      * specified data.

src/Set.php

@@ -40,6 +40,11 @@
  */
 class Set extends AbstractSet
 {
+    /**
+     * @psalm-suppress NonInvariantDocblockPropertyType
+     */
+    protected string $collection = self::class;
+
     /**
      * Constructs a set object of the specified type, optionally with the
      * specified data.

tests/CollectionTest.php

@@ -74,6 +74,13 @@ public function testAdd(): void
         $this->assertTrue($collection->add($this->faker->numberBetween()));
     }
 
+    public function testMapWillReturnANewCollection(): void
+    {
+        $collection = (new Collection('integer', [4, 2]))->map(fn ($value) => $value);
+
+        $this->assertInstanceOf(Collection::class, $collection);
+    }
+
     public function testAddMayAddSameObjectMultipleTimes(): void
     {
         $expectedCount = 4;

tests/SetTest.php

@@ -86,6 +86,26 @@ public function testMergingSets(): void
         $this->assertSame(['X', 'Y', 'Z'], $set3->toArray());
     }
 
+    public function testDuplicatesViaMap(): void
+    {
+        $this->assertTrue($this->set->add(100));
+        $this->assertTrue($this->set->add(200));
+
+        $set = $this->set->map(fn () => 200);
+
+        $this->assertSame([200], $set->toArray());
+    }
+
+    public function testMapReturnsANewSet(): void
+    {
+        $this->assertTrue($this->set->add(100));
+        $this->assertTrue($this->set->add(200));
+
+        $set = $this->set->map(fn ($value) => $value);
+
+        $this->assertInstanceOf(Set::class, $set);
+    }
+
     public function testMergingSetsOfObjects(): void
     {
         $obj1 = new Foo();