From c5a3f28fad4e379bd305085fc2c28e8df450c6a2 Mon Sep 17 00:00:00 2001
From: Kunal Mehta <kunalm@fb.com>
Date: Mon, 9 Oct 2017 15:22:48 -0700
Subject: [PATCH] Dict\flatten

Summary: Adding for parity with `{Keyset, Vec}\flatten`.

Reviewed By: fredemmott

Differential Revision: D6011560

fbshipit-source-id: 3527e9e5358a6795242f56dc5dd6ffe34e4a9cad
---
 src/dict/combine.php             |  8 +---
 src/dict/transform.php           | 19 ++++++++
 tests/dict/DictTransformTest.php | 77 ++++++++++++++++++++++++++++++++
 3 files changed, 97 insertions(+), 7 deletions(-)

diff --git a/src/dict/combine.php b/src/dict/combine.php
index 2b12ecc5..d4addf49 100644
--- a/src/dict/combine.php
+++ b/src/dict/combine.php
@@ -41,11 +41,5 @@ function associate<Tk as arraykey, Tv>(
 function merge<Tk, Tv>(
   KeyedTraversable<Tk, Tv> ...$traversables
 ): dict<Tk, Tv> {
-  $result = dict[];
-  foreach ($traversables as $traversable) {
-    foreach ($traversable as $key => $value) {
-      $result[$key] = $value;
-    }
-  }
-  return $result;
+  return namespace\flatten($traversables);
 }
diff --git a/src/dict/transform.php b/src/dict/transform.php
index c2dd018d..0c75486c 100644
--- a/src/dict/transform.php
+++ b/src/dict/transform.php
@@ -47,6 +47,25 @@ function count_values<Tv as arraykey>(
   return $result;
 }
 
+/**
+ * Returns a new dict formed by merging the KeyedTraversable elements of the
+ * given Traversable. In the case of duplicate keys, later values will overwrite
+ * the previous ones.
+ *
+ * For a fixed number of KeyedTraversables, see `Dict\merge`.
+ */
+function flatten<Tk, Tv>(
+  Traversable<KeyedTraversable<Tk, Tv>> $traversables,
+): dict<Tk, Tv> {
+  $result = dict[];
+  foreach ($traversables as $traversable) {
+    foreach ($traversable as $key => $value) {
+      $result[$key] = $value;
+    }
+  }
+  return $result;
+}
+
 /**
  * Returns a new dict where all the given keys map to the given value.
  */
diff --git a/tests/dict/DictTransformTest.php b/tests/dict/DictTransformTest.php
index 5c9538b3..cb0ad4b8 100644
--- a/tests/dict/DictTransformTest.php
+++ b/tests/dict/DictTransformTest.php
@@ -136,6 +136,83 @@ public function testFillKeys<Tk as arraykey, Tv>(
     expect(Dict\fill_keys($keys, $value))->toBeSame($expected);
   }
 
+  public static function provideTestFlatten(): array<mixed> {
+    return array(
+      tuple(
+        array(),
+        dict[],
+      ),
+      tuple(
+        array(
+          array(
+            'one' => 'one',
+            'two' => 'two',
+          ),
+          array(
+            'three' => 'three',
+            'one' => 3,
+          ),
+          Map {
+            'four' => null,
+          },
+        ),
+        dict[
+          'one' => 3,
+          'two' => 'two',
+          'three' => 'three',
+          'four' => null,
+        ],
+      ),
+      tuple(
+        array(
+          HackLibTestTraversables::getKeyedIterator(array(
+            'foo' => 'foo',
+            'bar' => 'bar',
+            'baz' => array(1, 2, 3),
+          )),
+          dict[
+            'bar' => 'barbar',
+          ],
+          Vector {'I should feel bad for doing this', 'But yolo'},
+          array(
+            '1' => 'gross array behavior',
+          ),
+          Set {'bloop'},
+        ),
+        dict[
+          'foo' => 'foo',
+          'bar' => 'barbar',
+          'baz' => array(1, 2, 3),
+          0 => 'I should feel bad for doing this',
+          1 => 'gross array behavior',
+          'bloop' => 'bloop',
+        ],
+      ),
+      tuple(
+        HackLibTestTraversables::getIterator(array(
+          vec['zero'],
+          array(1 => 'one'),
+          dict[2 => 'two'],
+          Map {3 => 'three'},
+        )),
+        dict[
+          0 => 'zero',
+          1 => 'one',
+          2 => 'two',
+          3 => 'three',
+        ],
+      ),
+    );
+  }
+
+  /** @dataProvider provideTestFlatten */
+  public function testFlatten<Tk, Tv>(
+    Traversable<KeyedTraversable<Tk, Tv>> $traversables,
+    dict<Tk, Tv> $expected,
+  ): void {
+    expect(Dict\flatten($traversables))->toBeSame($expected);
+  }
+
   public static function provideTestFlip(): array<mixed> {
     return array(
       tuple(