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/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program 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
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include "mongo/config.h"
#include <cstring>
#include <type_traits>
#include "mongo/base/error_codes.h"
#include "mongo/base/static_assert.h"
#include "mongo/base/status.h"
#include "mongo/base/status_with.h"
namespace mongo {
struct DataType {
// Second template parameter allows templatized SFINAE specialization.
//
// Something like:
// template <typename T, typename std::enable_if<std::is_CONDITION<T>::value>::type>
// struct Handler { ... };
//
// That would allow you to constrain your specialization to all T's
// that std::is_CONDITION<T>
//
// Again, note that you probably don't ever want to use this second
// parameter for anything. If you're not interested in template meta
// programming to duck type in a specialization, you can pretend that
// this just says template <typename T>.
template <typename T, typename = void>
struct Handler {
static void unsafeLoad(T* t, const char* ptr, size_t* advanced) {
#if MONGO_HAVE_STD_IS_TRIVIALLY_COPYABLE
MONGO_STATIC_ASSERT_MSG(std::is_trivially_copyable<T>::value,
"The generic DataType implementation requires values to be "
"trivially copyable. You may specialize the template to use it "
"with other types.");
#endif
if (t) {
std::memcpy(t, ptr, sizeof(T));
}
if (advanced) {
*advanced = sizeof(T);
}
}
static Status load(
T* t, const char* ptr, size_t length, size_t* advanced, std::ptrdiff_t debug_offset) {
if (sizeof(T) > length) {
return DataType::makeTrivialLoadStatus(sizeof(T), length, debug_offset);
}
unsafeLoad(t, ptr, advanced);
return Status::OK();
}
static void unsafeStore(const T& t, char* ptr, size_t* advanced) {
#if MONGO_HAVE_STD_IS_TRIVIALLY_COPYABLE
MONGO_STATIC_ASSERT_MSG(std::is_trivially_copyable<T>::value,
"The generic DataType implementation requires values to be "
"trivially copyable. You may specialize the template to use it "
"with other types.");
#endif
if (ptr) {
std::memcpy(ptr, &t, sizeof(T));
}
if (advanced) {
*advanced = sizeof(T);
}
}
static Status store(
const T& t, char* ptr, size_t length, size_t* advanced, std::ptrdiff_t debug_offset) {
if (sizeof(T) > length) {
return DataType::makeTrivialStoreStatus(sizeof(T), length, debug_offset);
}
unsafeStore(t, ptr, advanced);
return Status::OK();
}
// It may be useful to specialize this for types that aren't natively
// default constructible. Otherwise there's no way for us to support
// that body of types (other than wrapping them with another tagged
// type). Also, this guarantees value/aggregate initialization, which
// guarantees no uninitialized memory leaks from load's, which gcc
// otherwise can't seem to see.
static T defaultConstruct() {
return T{};
}
};
// The following dispatch functions don't just save typing, they also work
// around what seems like template type deduction bugs (for template
// specializations) in gcc. I.e. for sufficiently complicated workflows (a
// specialization for tuple), going through dispatch functions compiles on
// gcc 4.9 and using DataType<T> does not.
// We return a status and take an out pointer so that we can:
//
// 1. Run a load without returning a value (I.e. skip / validate)
// 2. Load directly into a remote structure, rather than forcing moves of
// possibly large objects
template <typename T>
static Status load(
T* t, const char* ptr, size_t length, size_t* advanced, std::ptrdiff_t debug_offset) {
return Handler<T>::load(t, ptr, length, advanced, debug_offset);
}
template <typename T>
static Status store(
const T& t, char* ptr, size_t length, size_t* advanced, std::ptrdiff_t debug_offset) {
return Handler<T>::store(t, ptr, length, advanced, debug_offset);
}
template <typename T>
static void unsafeLoad(T* t, const char* ptr, size_t* advanced) {
Handler<T>::unsafeLoad(t, ptr, advanced);
}
template <typename T>
static void unsafeStore(const T& t, char* ptr, size_t* advanced) {
Handler<T>::unsafeStore(t, ptr, advanced);
}
template <typename T>
static T defaultConstruct() {
return Handler<T>::defaultConstruct();
}
static Status makeTrivialStoreStatus(size_t sizeOfT, size_t length, size_t debug_offset);
static Status makeTrivialLoadStatus(size_t sizeOfT, size_t length, size_t debug_offset);
};
} // namespace mongo
// Force the visibility of the DataType::Handler specializations.
#define MONGO_BASE_DATA_TYPE_H_INCLUDE_HANDSHAKE_
#include "mongo/base/data_type_string_data.h"
#undef MONGO_BASE_DATA_TYPE_H_INCLUDE_HANDSHAKE_
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