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/*
* Copyright 2017 The Native Object Protocols Authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef LIBNOP_INCLUDE_NOP_BASE_VARIANT_H_
#define LIBNOP_INCLUDE_NOP_BASE_VARIANT_H_
#include <nop/base/encoding.h>
#include <nop/types/variant.h>
namespace nop {
//
// Variant<Ts...> encoding format:
//
// +-----+---------+-----------+
// | VAR | INT32:I | ELEMENT I |
// +-----+---------+-----------+
//
// Elements are expected to be valid encodings for their element type.
//
// EmptyVariant encoding format:
//
// +-----+
// | NIL |
// +-----+
//
// Therefore a Variant in the empty state has this specific encoding:
//
// +-----+----+-----+
// | VAR | -1 | NIL |
// +-----+----+-----+
//
template <>
struct Encoding<EmptyVariant> : EncodingIO<EmptyVariant> {
static constexpr EncodingByte Prefix(EmptyVariant /*value*/) {
return EncodingByte::Nil;
}
static constexpr std::size_t Size(EmptyVariant value) {
return BaseEncodingSize(Prefix(value));
}
static constexpr bool Match(EncodingByte prefix) {
return prefix == EncodingByte::Nil;
}
template <typename Writer>
static constexpr Status<void> WritePayload(EncodingByte /*prefix*/,
EmptyVariant /*value*/,
Writer* /*writer*/) {
return {};
}
template <typename Reader>
static constexpr Status<void> ReadPayload(EncodingByte /*prefix*/,
EmptyVariant* /*value*/,
Reader* /*reader*/) {
return {};
}
};
template <typename... Ts>
struct Encoding<Variant<Ts...>> : EncodingIO<Variant<Ts...>> {
using Type = Variant<Ts...>;
static constexpr EncodingByte Prefix(const Type& /*value*/) {
return EncodingByte::Variant;
}
static constexpr std::size_t Size(const Type& value) {
return BaseEncodingSize(Prefix(value)) +
Encoding<std::int32_t>::Size(value.index()) +
value.Visit([](const auto& element) {
using Element = typename std::decay<decltype(element)>::type;
return Encoding<Element>::Size(element);
});
}
static constexpr bool Match(EncodingByte prefix) {
return prefix == EncodingByte::Variant;
}
template <typename Writer>
static constexpr Status<void> WritePayload(EncodingByte /*prefix*/,
const Type& value,
Writer* writer) {
auto status = Encoding<std::int32_t>::Write(value.index(), writer);
if (!status)
return status;
return value.Visit([writer](const auto& element) {
using Element = typename std::decay<decltype(element)>::type;
return Encoding<Element>::Write(element, writer);
});
}
template <typename Reader>
static constexpr Status<void> ReadPayload(EncodingByte /*prefix*/,
Type* value, Reader* reader) {
std::int32_t type = 0;
auto status = Encoding<std::int32_t>::Read(&type, reader);
if (!status) {
return status;
} else if (type < Type::kEmptyIndex ||
type >= static_cast<std::int32_t>(sizeof...(Ts))) {
return ErrorStatus::UnexpectedVariantType;
}
value->Become(type);
return value->Visit([reader](auto&& element) {
using Element = typename std::decay<decltype(element)>::type;
return Encoding<Element>::Read(&element, reader);
});
}
};
} // namespace nop
#endif // LIBNOP_INCLUDE_NOP_BASE_VARIANT_H_
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