buffer.h c++17 improvements

1) ensure data is properly aligned
2) add move constructor (useful for zstrings)

src/util/buffer.h

@@ -27,19 +27,19 @@ Revision History:
 template<typename T, bool CallDestructors=true, unsigned INITIAL_SIZE=16>
 class buffer {
 protected:
-    T *      m_buffer;
-    unsigned m_pos;
-    unsigned m_capacity;
-    char     m_initial_buffer[INITIAL_SIZE * sizeof(T)];
-    
+    T *      m_buffer = reinterpret_cast<T*>(m_initial_buffer);
+    unsigned m_pos = 0;
+    unsigned m_capacity = INITIAL_SIZE;
+    typename std::aligned_storage<sizeof(T), alignof(T)>::type m_initial_buffer[INITIAL_SIZE];
+
     void free_memory() {
         if (m_buffer != reinterpret_cast<T*>(m_initial_buffer)) {
             dealloc_svect(m_buffer);
         }
     }
 
     void expand() {
-        static_assert(std::is_nothrow_move_constructible<T>::value, "");
+        static_assert(std::is_nothrow_move_constructible<T>::value);
         unsigned new_capacity = m_capacity << 1;
         T * new_buffer        = reinterpret_cast<T*>(memory::allocate(sizeof(T) * new_capacity));
         for (unsigned i = 0; i < m_pos; ++i) {
@@ -73,26 +73,29 @@ class buffer {
     typedef T * iterator;
     typedef const T * const_iterator;
 
-    buffer():
-        m_buffer(reinterpret_cast<T *>(m_initial_buffer)),
-        m_pos(0),
-        m_capacity(INITIAL_SIZE) {
-    }
+    buffer() = default;
 
-    buffer(const buffer & source):
-        m_buffer(reinterpret_cast<T *>(m_initial_buffer)),
-        m_pos(0),
-        m_capacity(INITIAL_SIZE) {
-        unsigned sz = source.size();
-        for(unsigned i = 0; i < sz; i++) {
+    buffer(const buffer & source) {
+        for (unsigned i = 0, sz = source.size(); i < sz; ++i) {
             push_back(source.m_buffer[i]);
         }
     }
-
-    buffer(unsigned sz, const T & elem):
-        m_buffer(reinterpret_cast<T *>(m_initial_buffer)),
-        m_pos(0),
-        m_capacity(INITIAL_SIZE) {
+
+    buffer(buffer && source) {
+        if (source.m_buffer == reinterpret_cast<T*>(source.m_initial_buffer)) {
+            for (unsigned i = 0, sz = source.size(); i < sz; ++i) {
+                push_back(std::move(source.m_buffer[i]));
+            }
+        } else {
+            m_pos           = source.m_pos;
+            m_capacity      = source.m_capacity;
+            m_buffer        = source.m_buffer;
+            source.m_buffer = reinterpret_cast<T*>(source.m_initial_buffer);
+            source.m_pos    = 0;
+        }
+    }
+
+    buffer(unsigned sz, const T & elem) {
         for (unsigned i = 0; i < sz; i++) {
             push_back(elem);
         }