Allow to define value mapper for toMap collector (#87)

* Remove to array casts

* Allow to define value mapper for toMap collector

Author: akondas

src/Collection/GenericList.php

@@ -79,8 +79,8 @@ public function map(callable $mapper): self
     public function flatMap(callable $mapper)
     {
         $list = self::empty();
-        foreach ($this->toArray() as $value) {
-            foreach ($mapper($value)->toArray() as $mapped) {
+        foreach ($this as $value) {
+            foreach ($mapper($value) as $mapped) {
                 $list = $list->prepend($mapped);
             }
         }

src/Collection/Stream/Collectors.php

@@ -38,15 +38,19 @@ public static function toSet(): Collector
 
     /**
      * @template T
+     * @template U
      *
-     * @param callable(T):string $keyProvider
+     * @param callable(T):string $keyMapper
+     * @param ?callable(T):U     $valueMapper
      *
      * @return Collector<T,Map>
      */
-    public static function toMap(callable $keyProvider): Collector
+    public static function toMap(callable $keyMapper, ?callable $valueMapper = null): Collector
     {
-        return GenericCollector::of(Map::empty(), /** @param T $value */ function (Map $map, $value) use ($keyProvider): Map {
-            return $map->put($keyProvider($value), $value);
+        $valueMapper ??= fn ($value) => $value;
+
+        return GenericCollector::of(Map::empty(), /** @param T $value */ function (Map $map, $value) use ($keyMapper, $valueMapper): Map {
+            return $map->put($keyMapper($value), $valueMapper($value));
         });
     }
 

tests/Collection/Stream/CollectorsTest.php

@@ -27,13 +27,25 @@ public function testToSetCollector(): void
         self::assertTrue(Set::of(1, 2, 3, 4, 5)->equals($set));
     }
 
-    public function testToMapCollector(): void
+    public function testToMapWithDefaultValueMapperCollector(): void
     {
-        $map = Stream::from(1)->take(3)->collect(Collectors::toMap(function (int $value): string {return (string) $value; }));
+        $map = Stream::from(1)->take(3)->collect(Collectors::toMap(
+            fn (int $value): string => (string) $value
+        ));
 
         self::assertTrue(Map::fromArray(['1' => 1, '2' => 2, '3' => 3])->equals($map));
     }
 
+    public function testToMapCollector(): void
+    {
+        $map = Stream::from(1)->take(3)->collect(Collectors::toMap(
+            fn (int $value): string => (string) $value,
+            fn (int $value): int => $value * 2,
+        ));
+
+        self::assertTrue(Map::fromArray(['1' => 2, '2' => 4, '3' => 6])->equals($map));
+    }
+
     public function testSummingCollector(): void
     {
         self::assertEquals(15, Stream::from(1)->take(5)->collect(Collectors::summing()));