1 files changed, 61 insertions, 32 deletions
diff --git a/src/util/WritableBuffer.hxx b/src/util/WritableBuffer.hxx
index 4e529cfad..7267813f5 100644
--- a/src/util/WritableBuffer.hxx
+++ b/src/util/WritableBuffer.hxx
@@ -32,7 +32,11 @@
 
 #include "Compiler.h"
 
-#include <stddef.h>
+#include <cstddef>
+
+#ifndef NDEBUG
+#include <assert.h>
+#endif
 
 /**
  * A reference to a memory area that is writable.
@@ -41,47 +45,72 @@
  */
 template<typename T>
 struct WritableBuffer {
-  typedef size_t size_type;
-  typedef T *pointer_type;
-  typedef const T *const_pointer_type;
-  typedef pointer_type iterator;
-  typedef const_pointer_type const_iterator;
+	typedef size_t size_type;
+	typedef T *pointer_type;
+	typedef const T *const_pointer_type;
+	typedef pointer_type iterator;
+	typedef const_pointer_type const_iterator;
+
+	pointer_type data;
+	size_type size;
+
+	WritableBuffer() = default;
 
-  pointer_type data;
-  size_type size;
+	constexpr WritableBuffer(std::nullptr_t):data(nullptr), size(0) {}
 
-  WritableBuffer() = default;
+	constexpr WritableBuffer(pointer_type _data, size_type _size)
+		:data(_data), size(_size) {}
 
-  constexpr WritableBuffer(pointer_type _data, size_type _size)
-    :data(_data), size(_size) {}
+	constexpr static WritableBuffer Null() {
+		return { nullptr, 0 };
+	}
+
+	/**
+	 * Cast a WritableBuffer<void> to a WritableBuffer<T>.  A "void"
+	 * buffer records its size in bytes, and when casting to "T",
+	 * the assertion below ensures that the size is a multiple of
+	 * sizeof(T).
+	 */
+#ifdef NDEBUG
+	constexpr
+#endif
+	static WritableBuffer<T> FromVoid(WritableBuffer<void> other) {
+		static_assert(sizeof(T) > 0, "Empty base type");
+#ifndef NDEBUG
+		assert(other.size % sizeof(T) == 0);
+#endif
+		return WritableBuffer<T>(pointer_type(other.data),
+				      other.size / sizeof(T));
+	}
 
-  constexpr static WritableBuffer Null() {
-    return { nullptr, 0 };
-  }
+	constexpr WritableBuffer<void> ToVoid() const {
+		static_assert(sizeof(T) > 0, "Empty base type");
+		return WritableBuffer<void>(data, size * sizeof(T));
+	}
 
-  constexpr bool IsNull() const {
-    return data == nullptr;
-  }
+	constexpr bool IsNull() const {
+		return data == nullptr;
+	}
 
-  constexpr bool IsEmpty() const {
-    return size == 0;
-  }
+	constexpr bool IsEmpty() const {
+		return size == 0;
+	}
 
-  constexpr iterator begin() const {
-    return data;
-  }
+	constexpr iterator begin() const {
+		return data;
+	}
 
-  constexpr iterator end() const {
-    return data + size;
-  }
+	constexpr iterator end() const {
+		return data + size;
+	}
 
-  constexpr const_iterator cbegin() const {
-    return data;
-  }
+	constexpr const_iterator cbegin() const {
+		return data;
+	}
 
-  constexpr const_iterator cend() const {
-    return data + size;
-  }
+	constexpr const_iterator cend() const {
+		return data + size;
+	}
 };
 
 #endif