LazyConstructor

2026-10-18 02:03:34 +08:00 · 2014-03-08 15:19:41 +04:00
parent bc065ee3c4
commit fd454a77f8
2 changed files with 206 additions and 0 deletions
@@ -0,0 +1,145 @@
+/*
+ * Copyright (C) 2014 Pavel Kirienko <pavel.kirienko@gmail.com>
+ */
+
+#pragma once
+
+#include <cstdlib>
+#include <cassert>
+#include <stdexcept>
+
+namespace uavcan
+{
+
+template <typename T>
+class LazyConstructor
+{
+    unsigned char data_[sizeof(T)] __attribute__((aligned(16)));  // TODO: compiler-independent alignment
+    T* ptr_;
+
+    void failure() const
+    {
+#if UAVCAN_EXCEPTIONS
+        throw std::logic_error(typeid(*this).name());
+#else
+        assert(0);
+        std::abort();
+#endif
+    }
+
+    void ensureConstructed() const
+    {
+        if (!ptr_)
+            failure();
+    }
+
+    void ensureNotConstructed() const
+    {
+        if (ptr_)
+            failure();
+    }
+
+public:
+    LazyConstructor()
+    : ptr_(NULL)
+    { }
+
+    LazyConstructor(const LazyConstructor<T>& rhs)
+    : ptr_(NULL)
+    {
+        if (rhs)
+            construct(*rhs);  // Invoke copy constructor
+    }
+
+    ~LazyConstructor() { destroy(); }
+
+    LazyConstructor<T>& operator=(const LazyConstructor<T>& rhs)
+    {
+        destroy();
+        if (rhs)
+            construct(*rhs);  // Invoke copy constructor
+        return *this;
+    }
+
+    bool isConstructed() const { return ptr_ != NULL; }
+
+    operator T*() const { return ptr_; }
+
+    const T* operator->() const { ensureConstructed(); return ptr_; }
+    T*       operator->()       { ensureConstructed(); return ptr_; }
+
+    const T& operator*() const { ensureConstructed(); return *ptr_; }
+    T&       operator*()       { ensureConstructed(); return *ptr_; }
+
+    void destroy()
+    {
+        if (ptr_)
+            ptr_->~T();
+        ptr_ = NULL;
+    }
+
+    void construct()
+    {
+        ensureNotConstructed();
+        ptr_ = new (static_cast<void*>(data_)) T();
+    }
+
+// MAX_ARGS = 6
+// TEMPLATE = '''
+//     template <%s>
+//     void construct(%s)
+//     {
+//         ensureNotConstructed();
+//         ptr_ = new (static_cast<void*>(data_)) T(%s);
+//     }'''
+// for nargs in range(1, MAX_ARGS + 1):
+//     nums = [(x + 1) for x in range(nargs)]
+//     l1 = ['typename P%d' % x for x in nums]
+//     l2 = ['P%d p%d' % (x, x) for x in nums]
+//     l3 = ['p%d' % x for x in nums]
+//     print(TEMPLATE % (', '.join(l1), ', '.join(l2), ', '.join(l3)))
+
+    template <typename P1>
+    void construct(P1 p1)
+    {
+        ensureNotConstructed();
+        ptr_ = new (static_cast<void*>(data_)) T(p1);
+    }
+
+    template <typename P1, typename P2>
+    void construct(P1 p1, P2 p2)
+    {
+        ensureNotConstructed();
+        ptr_ = new (static_cast<void*>(data_)) T(p1, p2);
+    }
+
+    template <typename P1, typename P2, typename P3>
+    void construct(P1 p1, P2 p2, P3 p3)
+    {
+        ensureNotConstructed();
+        ptr_ = new (static_cast<void*>(data_)) T(p1, p2, p3);
+    }
+
+    template <typename P1, typename P2, typename P3, typename P4>
+    void construct(P1 p1, P2 p2, P3 p3, P4 p4)
+    {
+        ensureNotConstructed();
+        ptr_ = new (static_cast<void*>(data_)) T(p1, p2, p3, p4);
+    }
+
+    template <typename P1, typename P2, typename P3, typename P4, typename P5>
+    void construct(P1 p1, P2 p2, P3 p3, P4 p4, P5 p5)
+    {
+        ensureNotConstructed();
+        ptr_ = new (static_cast<void*>(data_)) T(p1, p2, p3, p4, p5);
+    }
+
+    template <typename P1, typename P2, typename P3, typename P4, typename P5, typename P6>
+    void construct(P1 p1, P2 p2, P3 p3, P4 p4, P5 p5, P6 p6)
+    {
+        ensureNotConstructed();
+        ptr_ = new (static_cast<void*>(data_)) T(p1, p2, p3, p4, p5, p6);
+    }
+};
+
+}