Utils: Add "findOr(..., nullopt, ...)" function

findOr(nullopt) returns either a value or a std::nullopt for the first entry
in a container where the predicate returned true.

This makes it easy to write constructs like:

if (auto found = Utils::findOr(container, std::nullopt, [](auto){ ... condition ...}) {
...
}

Change-Id: I6f8f0f9c0d8486c32395123d8c2dcba427887189
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/libs/utils/algorithm.h

@@ -82,6 +82,10 @@ template<typename T, typename R, typename S>
 Q_REQUIRED_RESULT typename T::value_type findOr(const T &container,
                                                 typename T::value_type other,
                                                 R S::*member);
+template<typename T, typename F>
+Q_REQUIRED_RESULT std::optional<typename T::value_type> findOr(const T &container,
+                                                               std::nullopt_t,
+                                                               F function);
 
 /////////////////////////
 // findOrDefault
@@ -473,6 +477,21 @@ typename T::value_type findOr(const T &container, typename T::value_type other,
     return findOr(container, other, std::mem_fn(member));
 }
 
+template<typename C, typename F>
+Q_REQUIRED_RESULT typename std::optional<typename C::value_type> findOr(const C &container,
+                                                                        std::nullopt_t,
+                                                                        F function)
+{
+    typename C::const_iterator begin = std::begin(container);
+    typename C::const_iterator end = std::end(container);
+
+    typename C::const_iterator it = std::find_if(begin, end, function);
+    if (it == end)
+        return std::nullopt;
+
+    return *it;
+}
+
 //////////////////
 // findOrDefault
 //////////////////

tests/auto/algorithm/tst_algorithm.cpp

@@ -476,6 +476,9 @@ void tst_Algorithm::findOr()
     std::vector<int> v1{1, 2, 3, 4};
     QCOMPARE(Utils::findOr(v1, 10, [](int i) { return i == 2; }), 2);
     QCOMPARE(Utils::findOr(v1, 10, [](int i) { return i == 5; }), 10);
+
+    QCOMPARE(Utils::findOr(v1, std::nullopt, [](int i) { return i == 5; }), std::nullopt);
+    QCOMPARE(Utils::findOr(v1, std::nullopt, [](int i) { return i == 3; }), 3);
 }
 
 void tst_Algorithm::findOrDefault()