From 154fe8d8034f238180418ce32ac18bd6ab6df14a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?M=C3=A5rten=20Nordheim?= <marten.nordheim@qt.io>
Date: Thu, 28 Nov 2024 13:08:25 +0100
Subject: [PATCH] QHash tryEmplace-try_emplace compat

Let users use either type

Change-Id: Ica22a329df679352ab828aa96102a30fc9eedf79
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
---
 src/corelib/tools/qhash.h                    | 36 +++++++++++++-------
 tests/auto/corelib/tools/qhash/tst_qhash.cpp | 28 +++++++++++++++
 2 files changed, 52 insertions(+), 12 deletions(-)

diff --git a/src/corelib/tools/qhash.h b/src/corelib/tools/qhash.h
index 7347a73f831..e544b5f870a 100644
--- a/src/corelib/tools/qhash.h
+++ b/src/corelib/tools/qhash.h
@@ -1255,6 +1255,24 @@ public:
     {
         QHash::iterator iterator;
         bool inserted;
+
+        TryEmplaceResult() = default;
+        // Generated SMFs are fine!
+        TryEmplaceResult(QHash::iterator it, bool b)
+            : iterator(it), inserted(b)
+        {
+        }
+
+        // Implicit conversion _from_ the return-type of try_emplace:
+        Q_IMPLICIT TryEmplaceResult(const std::pair<key_value_iterator, bool> &p)
+            : iterator(p.first.base()), inserted(p.second)
+        {
+        }
+        // Implicit conversion _to_ the return-type of try_emplace:
+        Q_IMPLICIT operator std::pair<key_value_iterator, bool>()
+        {
+            return { key_value_iterator(iterator), inserted };
+        }
     };
 
     iterator erase(const_iterator it)
@@ -1387,26 +1405,22 @@ public:
     template <typename... Args>
     std::pair<key_value_iterator, bool> try_emplace(const Key &key, Args &&...args)
     {
-        auto r = tryEmplace_impl(key, std::forward<Args>(args)...);
-        return {key_value_iterator(r.iterator), r.inserted};
+        return tryEmplace_impl(key, std::forward<Args>(args)...);
     }
     template <typename... Args>
     std::pair<key_value_iterator, bool> try_emplace(Key &&key, Args &&...args)
     {
-        auto r = tryEmplace_impl(std::move(key), std::forward<Args>(args)...);
-        return {key_value_iterator(r.iterator), r.inserted};
+        return tryEmplace_impl(std::move(key), std::forward<Args>(args)...);
     }
     template <typename... Args>
     key_value_iterator try_emplace(const_iterator /*hint*/, const Key &key, Args &&...args)
     {
-        auto r = tryEmplace_impl(key, std::forward<Args>(args)...);
-        return key_value_iterator(r.iterator);
+        return key_value_iterator(tryEmplace_impl(key, std::forward<Args>(args)...).iterator);
     }
     template <typename... Args>
     key_value_iterator try_emplace(const_iterator /*hint*/, Key &&key, Args &&...args)
     {
-        auto r = tryEmplace_impl(std::move(key), std::forward<Args>(args)...);
-        return key_value_iterator(r.iterator);
+        return key_value_iterator(tryEmplace_impl(std::move(key), std::forward<Args>(args)...).iterator);
     }
 
 private:
@@ -1557,14 +1571,12 @@ public:
     template <typename K, typename... Args, if_heterogeneously_searchable<K> = true, if_key_constructible_from<K> = true>
     std::pair<key_value_iterator, bool> try_emplace(K &&key, Args &&...args)
     {
-        auto r = tryEmplace_impl(std::forward<K>(key), std::forward<Args>(args)...);
-        return { key_value_iterator(r.iterator), r.inserted };
+        return tryEmplace_impl(std::forward<K>(key), std::forward<Args>(args)...);
     }
     template <typename K, typename... Args, if_heterogeneously_searchable<K> = true, if_key_constructible_from<K> = true>
     key_value_iterator try_emplace(const_iterator /*hint*/, K &&key, Args &&...args)
     {
-        auto r = tryEmplace_impl(std::forward<K>(key), std::forward<Args>(args)...);
-        return key_value_iterator(r.iterator);
+        return key_value_iterator(tryEmplace_impl(std::forward<K>(key), std::forward<Args>(args)...).iterator);
     }
 };
 
diff --git a/tests/auto/corelib/tools/qhash/tst_qhash.cpp b/tests/auto/corelib/tools/qhash/tst_qhash.cpp
index bd8913a39e6..e8bcdb275fe 100644
--- a/tests/auto/corelib/tools/qhash/tst_qhash.cpp
+++ b/tests/auto/corelib/tools/qhash/tst_qhash.cpp
@@ -2862,6 +2862,34 @@ void tst_QHash::tryEmplace()
         QCOMPARE(hash[0], 0);
         QVERIFY(!inserted2);
         QCOMPARE(it->second, 0);
+
+        using KVIterator = decltype(hash)::key_value_iterator;
+        using PairReturn = std::pair<KVIterator, bool>; // Return-value of try_emplace
+
+        // Handle conversion _from_ the try_emplace return type.
+        QHash<int, int>::TryEmplaceResult t = hash.try_emplace(2, 2);
+        QCOMPARE(t.inserted, true);
+        QCOMPARE(t.iterator.value(), 2);
+        QCOMPARE(hash.size(), 3);
+
+        t = hash.try_emplace(2, -1);
+        QCOMPARE(t.inserted, false);
+        QCOMPARE(t.iterator.value(), 2);
+        QCOMPARE(hash.size(), 3);
+
+        // Handle conversion _to_ the try_emplace return type.
+        PairReturn p = hash.tryEmplace(1, -1);
+        QCOMPARE_NE(p.first, hash.keyValueEnd());
+        QCOMPARE(hash.size(), 3);
+
+        QVERIFY(!p.second);
+        QCOMPARE(p.first->second, 1);
+
+        p = hash.try_emplace(cref, -1);
+        QCOMPARE_NE(p.first, hash.keyValueEnd());
+        QCOMPARE(hash.size(), 3);
+        QVERIFY(!p.second);
+        QCOMPARE(p.first->second, 0);
     }
     {
         // Make sure any kind of resize is properly handled