From 5df61f19dc6486e2282fc7e61c46e4dc3e92549d Mon Sep 17 00:00:00 2001
From: Timothy Rae <perceptualchaos2@gmail.com>
Date: Mon, 23 Jan 2017 17:46:37 +0900
Subject: [PATCH] Introduce parented_ptr<T> class which is owned by the QT
 object tree

---
 src/util/parented_ptr.h | 88 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 88 insertions(+)
 create mode 100644 src/util/parented_ptr.h

diff --git a/src/util/parented_ptr.h b/src/util/parented_ptr.h
new file mode 100644
index 000000000000..7151570fc2c8
--- /dev/null
+++ b/src/util/parented_ptr.h
@@ -0,0 +1,88 @@
+#ifndef UTIL_PARENTED_POINTER_H
+#define UTIL_PARENTED_POINTER_H
+
+#include <memory>
+#include "util/assert.h"
+
+
+/**
+ * Use this wrapper class to clearly represent a pointer that is owned by the QT object tree.
+ * Objects which both derive from QObject AND have a parent object, have their lifetime governed by the QT object tree, 
+ * and thus pointers to such objects do not need to be deleted when they go  out of scope.
+**/
+template <typename T>
+class parented_ptr {
+  public:
+    explicit parented_ptr(T* t) : m_pObject(t) {
+        DEBUG_ASSERT(t->parent() != nullptr);
+    }
+
+    /* If U* is convertible to T* then we also want parented_ptr<U> convertible to parented_ptr<T> */
+    template <typename U>
+    parented_ptr(const parented_ptr<U>& u, typename std::enable_if<std::is_convertible<U*, T*>::value, void>::type * = 0) 
+            : m_pObject(u.get()) {
+        DEBUG_ASSERT(u->parent() != nullptr);
+    }
+
+    parented_ptr() : m_pObject(nullptr) {}
+
+    ~parented_ptr() = default;
+
+    T* get() const {
+        return m_pObject;
+    }
+
+    T& operator* () const {
+        return *m_pObject;
+    }
+
+    T* operator-> () const {
+        return m_pObject;
+    }
+
+    bool operator== (const parented_ptr& other) const {
+        return m_pObject == other.m_ptr;
+    }
+
+    bool operator== (const T* other) const {
+        return m_pObject == other;
+    }
+
+    bool operator!= (const parented_ptr& other) const {
+        return m_pObject != other.m_pObject;
+    }
+
+    bool operator!= (const T* other) const {
+        return m_pObject != other;
+    }
+
+    operator bool() const {
+        return m_pObject != nullptr;
+    }
+
+    /* 
+     * If U* is convertible to T* then we also want parented_ptr<U> assignable to parented_ptr<T> 
+     * E.g. parented_ptr<Base> base = make_parented<Derived>(); should work as expected.
+     */
+    template <typename U>
+    typename std::enable_if<std::is_convertible<U*, T*>::value, parented_ptr<T>&>::type
+            operator=(const parented_ptr<U>& p) {
+        m_pObject = p.get();
+        return *this;
+    }
+
+  private:
+    T* m_pObject;
+};
+
+namespace {
+
+template<typename T, typename... Args>
+inline parented_ptr<T> make_parented(Args&&... args) {
+    return parented_ptr<T>(new T(std::forward<Args>(args)...));
+}
+
+
+} // namespace
+
+#endif /* UTIL_PARENTED_POINTER_H */