Write interface for new serialization system

contrib/epee/include/serialization/wire/wrapper/defaulted.h

@@ -0,0 +1,77 @@
+// Copyright (c) 2021-2023, The Monero Project
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without modification, are
+// permitted provided that the following conditions are met:
+//
+// 1. Redistributions of source code must retain the above copyright notice, this list of
+//    conditions and the following disclaimer.
+//
+// 2. Redistributions in binary form must reproduce the above copyright notice, this list
+//    of conditions and the following disclaimer in the documentation and/or other
+//    materials provided with the distribution.
+//
+// 3. Neither the name of the copyright holder nor the names of its contributors may be
+//    used to endorse or promote products derived from this software without specific
+//    prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
+// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#pragma once
+
+#include <functional>
+#include <utility>
+
+#include "serialization/wire/field.h"
+#include "serialization/wire/traits.h"
+
+//! An optional field that is omitted when a default value is used
+#define WIRE_FIELD_DEFAULTED(name, default_)                            \
+  ::wire::optional_field( #name , ::wire::defaulted(std::ref( self . name ), default_ ))
+
+namespace wire
+{
+  /*! A wrapper that tells `wire::writer`s to skip field generation when default
+    value, and tells `wire::reader`s to use default value when field not present. */
+  template<typename T, typename U>
+  struct defaulted_
+  {
+    using value_type = unwrap_reference_t<T>;
+
+    T value;
+    U default_;
+
+    constexpr const value_type& get_value() const noexcept { return value; }
+    value_type& get_value() noexcept { return value; }
+
+    // concept requirements for optional fields
+
+    constexpr explicit operator bool() const { return get_value() != default_; }
+    value_type& emplace() noexcept { return get_value(); }
+
+    constexpr const value_type& operator*() const noexcept { return get_value(); }
+    value_type& operator*() noexcept { return get_value(); }
+
+    void reset() { get_value() = default_; }
+  };
+
+  //! Links `value` with `default_`.
+  template<typename T, typename U>
+  inline constexpr defaulted_<T, U> defaulted(T value, U default_)
+  {
+    return {std::move(value), std::move(default_)};
+  }
+
+  /* read/write functions not needed since `defaulted_` meets the concept
+     requirements for an optional type (optional fields are handled
+     directly by the generic read/write code because the field name is omitted
+     entirely when the value is "empty"). */
+} // wire