initial commit

tdutils/td/utils/as.h

@@ -0,0 +1,98 @@
+/*
+    This file is part of TON Blockchain Library.
+
+    TON Blockchain Library is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Lesser General Public License as published by
+    the Free Software Foundation, either version 2 of the License, or
+    (at your option) any later version.
+
+    TON Blockchain Library is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Lesser General Public License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with TON Blockchain Library.  If not, see <http://www.gnu.org/licenses/>.
+
+    Copyright 2017-2019 Telegram Systems LLP
+*/
+#pragma once
+
+#include <cstring>
+#include <type_traits>
+
+namespace td {
+
+namespace detail {
+
+template <class T>
+class As {
+ public:
+  explicit As(void *ptr) : ptr_(ptr) {
+  }
+
+  As(const As &new_value) = delete;
+  As &operator=(const As &) = delete;
+  As(As &&) = default;
+  As &operator=(As &&new_value) && {
+    std::memcpy(ptr_, new_value.ptr_, sizeof(T));
+    return *this;
+  }
+  ~As() = default;
+
+  As &operator=(T new_value) && {
+    std::memcpy(ptr_, &new_value, sizeof(T));
+    return *this;
+  }
+
+  operator T() const {
+    T res;
+    std::memcpy(&res, ptr_, sizeof(T));
+    return res;
+  }
+  bool operator==(const As &other) const {
+    return this->operator T() == other.operator T();
+  }
+
+ private:
+  void *ptr_;
+};
+
+template <class T>
+class ConstAs {
+ public:
+  explicit ConstAs(const void *ptr) : ptr_(ptr) {
+  }
+
+  operator T() const {
+    T res;
+    std::memcpy(&res, ptr_, sizeof(T));
+    return res;
+  }
+
+ private:
+  const void *ptr_;
+};
+
+}  // namespace detail
+
+// no std::is_trivially_copyable in libstdc++ before 5.0
+#if __GLIBCXX__
+#define TD_IS_TRIVIALLY_COPYABLE(T) __has_trivial_copy(T)
+#else
+#define TD_IS_TRIVIALLY_COPYABLE(T) std::is_trivially_copyable<T>::value
+#endif
+
+template <class ToT, class FromT,
+          std::enable_if_t<TD_IS_TRIVIALLY_COPYABLE(ToT) && TD_IS_TRIVIALLY_COPYABLE(FromT), int> = 0>
+detail::As<ToT> as(FromT *from) {
+  return detail::As<ToT>(from);
+}
+
+template <class ToT, class FromT,
+          std::enable_if_t<TD_IS_TRIVIALLY_COPYABLE(ToT) && TD_IS_TRIVIALLY_COPYABLE(FromT), int> = 0>
+const detail::ConstAs<ToT> as(const FromT *from) {
+  return detail::ConstAs<ToT>(from);
+}
+
+}  // namespace td