From 6f80025fe67cc3cf68ca700967e6920285fbd9da Mon Sep 17 00:00:00 2001
From: Moritz Bunkus <moritz@bunkus.org>
Date: Sat, 6 Jun 2015 15:40:16 +0200
Subject: [PATCH] list utils: implementation of first_of

---
 src/common/list_utils.h          | 18 ++++++++++++++++++
 tests/unit/common/list_utils.cpp | 15 +++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/src/common/list_utils.h b/src/common/list_utils.h
index 0a8cedaf1..eb6592e25 100644
--- a/src/common/list_utils.h
+++ b/src/common/list_utils.h
@@ -14,6 +14,8 @@
 #ifndef MTX_COMMON_LIST_UTILS_H
 #define MTX_COMMON_LIST_UTILS_H
 
+#include <boost/optional.hpp>
+
 namespace mtx {
 
 template<typename T>
@@ -73,6 +75,22 @@ none_of(std::function<bool(T const &)> pred,
   return !any_of<T, Trest...>(pred, val, rest...);
 }
 
+template<typename T>
+boost::optional<T>
+first_of(std::function<bool(T const &)> pred,
+       T const &val) {
+  return pred(val) ? val : boost::optional<T>{};
+}
+
+template<typename T,
+         typename... Trest>
+boost::optional<T>
+first_of(std::function<bool(T const &)> pred,
+       T const &val,
+       Trest... rest) {
+  return pred(val) ? val : first_of(pred, rest...);
+}
+
 }
 
 #endif  // MTX_COMMON_LIST_UTILS_H
diff --git a/tests/unit/common/list_utils.cpp b/tests/unit/common/list_utils.cpp
index 37732cab7..38b707c2b 100644
--- a/tests/unit/common/list_utils.cpp
+++ b/tests/unit/common/list_utils.cpp
@@ -6,6 +6,21 @@
 
 namespace {
 
+TEST(ListUtils, first_of) {
+  EXPECT_FALSE(mtx::first_of<int>([](int val) { return val > 43; }, 42));
+
+  EXPECT_TRUE(!!mtx::first_of<int>([](int val) { return val > 43; }, 48));
+  EXPECT_TRUE(!!mtx::first_of<int>([](int val) { return val > 43; }, 42, 54));
+  EXPECT_TRUE(!!mtx::first_of<int>([](int val) { return val > 43; }, 42, 41, 40, 39, 38, 12345));
+
+  EXPECT_EQ(48,    mtx::first_of<int>([](int val) { return val > 43; }, 48));
+  EXPECT_EQ(54,    mtx::first_of<int>([](int val) { return val > 43; }, 42, 54).get());
+  EXPECT_EQ(12345, mtx::first_of<int>([](int val) { return val > 43; }, 42, 41, 40, 39, 38, 12345).get());
+
+  EXPECT_TRUE(!!mtx::first_of<void *>([](void *p) { return !!p; }, static_cast<void *>(nullptr), reinterpret_cast<void *>(0x12345)));
+  EXPECT_EQ(reinterpret_cast<void *>(0x12345), mtx::first_of<void *>([](void *p) { return !!p; }, static_cast<void *>(nullptr), reinterpret_cast<void *>(0x12345)));
+}
+
 TEST(ListUtils, included_in) {
   EXPECT_TRUE(mtx::included_in(42, 42));
   EXPECT_TRUE(mtx::included_in(42, 54, 42, 48));