QTableGenerator: give some TLC to the sorting predicate

- Provide op()(uint[], QComposeTableElement) as well, since the
  standard (does|did) not specify in which order the two are called.
- Use std::lexicographical_compare to do the ... lexicographical
  comparison.
- Share code by calling a new op()(uint[], uint[]) overload from all
  other overloads.
- Mark all op() overloads const noexept.
- Rename from 'Compare' to 'ByKeys', as in 'sort(vector, ByKeys()))'.
- Replace a hand-rolled loop with std::equal.
- Replace a #define with a static constexpr variable.

Change-Id: I5ed487199916d0ae44ac38741fc95099bd2f8a22
Reviewed-by: Sune Vuorela <sune@vuorela.dk>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Milian Wolff <milian.wolff@kdab.com>

src/plugins/platforminputcontexts/compose/generator/qtablegenerator.cpp

@@ -645,6 +645,6 @@ void TableGenerator::orderComposeTable()
     // Stable-sorting to ensure that the item that appeared before the other in the
     // original container will still appear first after the sort. This property is
     // needed to handle the cases when user re-defines already defined key sequence
-    std::stable_sort(m_composeTable.begin(), m_composeTable.end(), Compare());
+    std::stable_sort(m_composeTable.begin(), m_composeTable.end(), ByKeys());
 }
 

src/plugins/platforminputcontexts/compose/generator/qtablegenerator.h

@@ -45,7 +45,9 @@
 #include <QtCore/QMap>
 #include <QtCore/QString>
 
-#define QT_KEYSEQUENCE_MAX_LEN 6
+#include <algorithm>
+
+static Q_CONSTEXPR int QT_KEYSEQUENCE_MAX_LEN = 6;
 
 //#define DEBUG_GENERATOR
 
@@ -65,25 +67,30 @@ Q_DECLARE_TYPEINFO(QComposeTableElement, Q_PRIMITIVE_TYPE);
 QT_END_NAMESPACE
 #endif
 
-class Compare
+struct ByKeys
 {
-public:
-    bool operator () (const QComposeTableElement &lhs, const uint rhs[QT_KEYSEQUENCE_MAX_LEN])
+    using uint_array = uint[QT_KEYSEQUENCE_MAX_LEN];
+    using result_type = bool;
+
+    bool operator()(const uint_array &lhs, const uint_array &rhs) const Q_DECL_NOTHROW
     {
-        for (size_t i = 0; i < QT_KEYSEQUENCE_MAX_LEN; i++) {
-            if (lhs.keys[i] != rhs[i])
-                return (lhs.keys[i] < rhs[i]);
-        }
-        return false;
+        return std::lexicographical_compare(lhs, lhs + QT_KEYSEQUENCE_MAX_LEN,
+                                            rhs, rhs + QT_KEYSEQUENCE_MAX_LEN);
     }
 
-    bool operator () (const QComposeTableElement &lhs, const QComposeTableElement &rhs)
+    bool operator()(const uint_array &lhs, const QComposeTableElement &rhs) const Q_DECL_NOTHROW
     {
-        for (size_t i = 0; i < QT_KEYSEQUENCE_MAX_LEN; i++) {
-            if (lhs.keys[i] != rhs.keys[i])
-                return (lhs.keys[i] < rhs.keys[i]);
-        }
-        return false;
+        return operator()(lhs, rhs.keys);
+    }
+
+    bool operator()(const QComposeTableElement &lhs, const uint_array &rhs) const Q_DECL_NOTHROW
+    {
+        return operator()(lhs.keys, rhs);
+    }
+
+    bool operator()(const QComposeTableElement &lhs, const QComposeTableElement &rhs) const Q_DECL_NOTHROW
+    {
+        return operator()(lhs.keys, rhs.keys);
     }
 };
 

src/plugins/platforminputcontexts/compose/qcomposeplatforminputcontext.cpp

@@ -155,11 +155,8 @@ void QComposeInputContext::update(Qt::InputMethodQueries q)
 
 static bool isDuplicate(const QComposeTableElement &lhs, const QComposeTableElement &rhs)
 {
-    for (size_t i = 0; i < QT_KEYSEQUENCE_MAX_LEN; i++) {
-        if (lhs.keys[i] != rhs.keys[i])
-            return false;
-    }
-    return true;
+    return std::equal(lhs.keys, lhs.keys + QT_KEYSEQUENCE_MAX_LEN,
+                      QT_MAKE_CHECKED_ARRAY_ITERATOR(rhs.keys, QT_KEYSEQUENCE_MAX_LEN));
 }
 
 bool QComposeInputContext::checkComposeTable()
@@ -182,7 +179,7 @@ bool QComposeInputContext::checkComposeTable()
     }
     Q_ASSERT(!m_composeTable.isEmpty());
     QVector<QComposeTableElement>::const_iterator it =
-            std::lower_bound(m_composeTable.constBegin(), m_composeTable.constEnd(), m_composeBuffer, Compare());
+            std::lower_bound(m_composeTable.constBegin(), m_composeTable.constEnd(), m_composeBuffer, ByKeys());
 
     // prevent dereferencing an 'end' iterator, which would result in a crash
     if (it == m_composeTable.constEnd())