From 89e55c5297e7b510ed04d7b126397bc61459c1f9 Mon Sep 17 00:00:00 2001
From: Sam Atkins <atkinssj@serenityos.org>
Date: Mon, 10 Apr 2023 17:27:16 +0100
Subject: [PATCH] AK+Tests: Add Vector::find_first_index_if()

---
 AK/Vector.h             | 9 +++++++++
 Tests/AK/TestVector.cpp | 8 ++++++++
 2 files changed, 17 insertions(+)

diff --git a/AK/Vector.h b/AK/Vector.h
index cb6a69830a0..3bf34b8d2a6 100644
--- a/AK/Vector.h
+++ b/AK/Vector.h
@@ -796,6 +796,15 @@ public:
         return {};
     }
 
+    template<typename TUnaryPredicate>
+    Optional<size_t> find_first_index_if(TUnaryPredicate&& finder) const
+    {
+        auto maybe_result = AK::find_if(begin(), end(), finder);
+        if (maybe_result == end())
+            return {};
+        return maybe_result.index();
+    }
+
     void reverse()
     {
         for (size_t i = 0; i < size() / 2; ++i)
diff --git a/Tests/AK/TestVector.cpp b/Tests/AK/TestVector.cpp
index 9e0c5f80674..6bf010b8b7b 100644
--- a/Tests/AK/TestVector.cpp
+++ b/Tests/AK/TestVector.cpp
@@ -423,6 +423,14 @@ TEST_CASE(should_find_index)
     EXPECT(!v.find_first_index(42).has_value());
 }
 
+TEST_CASE(should_find_predicate_index)
+{
+    Vector<int> v { 1, 2, 3, 4, 0, 6, 7, 8, 0, 0 };
+
+    EXPECT_EQ(4u, v.find_first_index_if([](auto const v) { return v == 0; }).value());
+    EXPECT(!v.find_first_index_if([](auto const v) { return v == 123; }).has_value());
+}
+
 TEST_CASE(should_contain_start)
 {
     // Tests whether value is found if at the start of the range.