TaskTree: Introduce LoopList

A wrapper around container with convenient
"const T *operator->() const" and "const T &operator*() const" methods.
They mimic the const_iterator API.
Simplifies the usages, as it enough not to capture just
LoopList element inside task handlers without a container itself.

For now it handles just QList container.
To be generalized later.

Change-Id: I10ea3903985cf51529ec5909ac7c19c524de7c68
Reviewed-by: hjk <hjk@qt.io>

src/libs/solutions/tasking/tasktree.cpp

@@ -1249,6 +1249,7 @@ public:
     }
 
     const std::optional<int> m_loopCount = {};
+    const Loop::ValueGetter m_valueGetter = {};
     const Loop::Condition m_condition = {};
     std::mutex m_threadDataMutex = {};
     // Use std::map on purpose, so that it doesn't invalidate references on modifications.
@@ -1260,12 +1261,12 @@ Loop::Loop()
     : m_loopData(new LoopData)
 {}
 
-Loop::Loop(int count)
+Loop::Loop(int count, const ValueGetter &valueGetter)
-    : m_loopData(new LoopData{count})
+    : m_loopData(new LoopData{count, valueGetter})
 {}
 
 Loop::Loop(const Condition &condition)
-    : m_loopData(new LoopData{{}, condition})
+    : m_loopData(new LoopData{{}, {}, condition})
 {}
 
 int Loop::iteration() const
@@ -1273,6 +1274,11 @@ int Loop::iteration() const
     return m_loopData->threadData().iteration();
 }
 
+const void *Loop::valuePtr() const
+{
+    return m_loopData->m_valueGetter(iteration());
+}
+
 using StoragePtr = void *;
 
 class StorageThreadData

src/libs/solutions/tasking/tasktree.h

@@ -6,6 +6,7 @@
 #include "tasking_global.h"
 
 #include <QObject>
+#include <QList>
 #include <QSharedPointer>
 
 #include <memory>
@@ -101,14 +102,17 @@ class TASKING_EXPORT Loop
 {
 public:
     using Condition = std::function<bool(int)>; // Takes iteration, called prior to each iteration.
+    using ValueGetter = std::function<const void *(int)>; // Takes iteration, returns ptr to ref.
 
     int iteration() const;
 
 protected:
     Loop(); // LoopForever
-    Loop(int count); // LoopRepeat
+    Loop(int count, const ValueGetter &valueGetter = {}); // LoopRepeat, LoopList
     Loop(const Condition &condition); // LoopUntil
 
+    const void *valuePtr() const;
+
 private:
     friend class ExecutionContextActivator;
     friend class TaskTreePrivate;
@@ -133,6 +137,15 @@ public:
     LoopUntil(const Condition &condition) : Loop(condition) {}
 };
 
+template <typename T>
+class LoopList final : public Loop
+{
+public:
+    LoopList(const QList<T> &list) : Loop(list.size(), [list](int i) { return &list.at(i); }) {}
+    const T *operator->() const { return static_cast<const T *>(valuePtr()); }
+    const T &operator*() const { return *static_cast<const T *>(valuePtr()); }
+};
+
 class TASKING_EXPORT StorageBase
 {
 private: