Equal.h

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#pragma once

#include <typeinfo>
#include <type_traits>

#include <algorithm>

#include <string>
#include <bitset>
#include <utility>
#include <tuple>
#include <memory>
#include <array>
#include <vector>
#include <deque>
#include <forward_list>
#include <list>
#include <set>
#include <unordered_set>
#include <map>
#include <unordered_map>

#include <cstddef>
#include <cmath>

#include <boost/shared_ptr.hpp>

#include "CondFormats/Serialization/interface/Serializable.h"

namespace cond {
namespace serialization {

template <typename T>
bool equal(const T & first, const T & second)
{
    // This function takes advantage of template argument deduction,
    // making it easier to use than the access<T> template.

    // It is also called by the access<T>::equal_() methods themselves
    // if they need to compare objects. This means all comparisons
    // pass by here.

    // Therefore, we could easily first check here whether the address of
    // the objects is the same or add debugging code. In our use case,
    // however, most of the objects will have different addresses.
    return access<T>::equal_(first, second);
}

template <typename T>
struct access<T, typename std::enable_if<std::is_integral<T>::value or std::is_enum<T>::value>::type>
{
    static bool equal_(const T first, const T second)
    {
        return first == second;
    }
};

template <typename T>
struct access<T, typename std::enable_if<std::is_floating_point<T>::value>::type>
{
    static bool equal_(const T first, const T second)
    {
        // TODO: we consider all NaNs to be equal -- should we even allow to serialize them?
        if (std::isnan(first) or std::isnan(second))
            return std::isnan(first) and std::isnan(second);

        if (std::isinf(first) or std::isinf(second))
            return std::isinf(first) and std::isinf(second) and std::signbit(first) == std::signbit(second);

        // TODO: consider expected precision for cross-platform serialization
        return first == second;
    }
};

template <>
struct access<std::string>
{
    static bool equal_(const std::string & first, const std::string & second)
    {
        return first == second;
    }
};

template <std::size_t N>
struct access<std::bitset<N>>
{
    static bool equal_(const std::bitset<N> & first, const std::bitset<N> & second)
    {
        return first == second;
    }
};

template <typename T, typename U>
struct access<std::pair<T, U>>
{
    static bool equal_(const std::pair<T, U> & first, const std::pair<T, U> & second)
    {
        return equal(first.first, second.first) and equal(first.second, second.second);
    }
};

template <std::size_t N, typename... Ts>
struct equal_tuple
{
    static bool equal_(const std::tuple<Ts...> & first, const std::tuple<Ts...> & second)
    {
        if (not equal(std::get<N - 1>(first), std::get<N - 1>(second)))
            return false;

        return equal_tuple<N - 1, Ts...>::equal_(first, second);
    }
};

template <typename... Ts>
struct equal_tuple<0, Ts...>
{
    static bool equal_(const std::tuple<Ts...> & first, const std::tuple<Ts...> & second)
    {
        return true;
    }
};

template <typename... Ts>
struct access<std::tuple<Ts...>>
{
    static bool equal_(const std::tuple<Ts...> & first, const std::tuple<Ts...> & second)
    {
        return equal_tuple<sizeof...(Ts), Ts...>::equal_(first, second);
    }
};

template <typename T>
struct access<T, typename std::enable_if<std::is_pointer<T>::value>::type>
{
    static bool equal_(const T first, const T second)
    {
        if (first == nullptr or second == nullptr)
            return first == second;

        // Compare the addresses first -- even if equal() does not
        // do it for all types, if we are serializing pointers we may
        // have some use case of containers of pointers to a small
        // set of real objects.
        return first == second or equal(*first, *second);
    }
};

#define equal_pointer(TYPE) \
template <typename T> \
struct access<TYPE<T>> \
{ \
    static bool equal_(const TYPE<T> & first, const TYPE<T> & second) \
    { \
        return equal(first.get(), second.get()); \
    } \
};

equal_pointer(std::unique_ptr);
equal_pointer(std::shared_ptr);
equal_pointer(boost::shared_ptr);
#undef equal_pointer

template <typename T, std::size_t N>
struct access<T[N]>
{
    static bool equal_(const T (&first)[N], const T (&second)[N])
    {
        for (std::size_t i = 0; i < N; ++i)
            if (not equal(first[i], second[i]))
                return false;
        return true;
    }
};

template <typename T, std::size_t N>
struct access<std::array<T, N>>
{
    static bool equal_(const std::array<T, N> & first, const std::array<T, N> & second)
    {
        for (std::size_t i = 0; i < N; ++i)
            if (not equal(first[i], second[i]))
                return false;
        return true;
    }
};

#define equal_sequence(TYPE) \
template <typename T> \
struct access<TYPE<T>> \
{ \
    static bool equal_(const TYPE<T> & first, const TYPE<T> & second) \
    { \
        return first.size() == second.size() && std::equal(first.cbegin(), first.cend(), second.cbegin(), \
            [](decltype(*first.cbegin()) a, decltype(a) b) -> bool { \
                return equal(a, b); \
            } \
        ); \
    } \
};

equal_sequence(std::vector);
equal_sequence(std::deque);
equal_sequence(std::list);
equal_sequence(std::set); // ordered
equal_sequence(std::multiset); // ordered
#undef equal_sequence

// forward_list is a sequence, but does not provide size() and we are not yet
// in C++14 so we cannot use the 4 iterators version of std::equal()
template <typename T>
struct access<std::forward_list<T>>
{
    static bool equal_(const std::forward_list<T> & first, const std::forward_list<T> & second)
    {
        auto first_it = first.cbegin();
        auto second_it = second.cbegin();

        while (first_it != first.cend() and second_it != second.cend()) {
            if (not equal(*first_it, *second_it))
                return false;
            first_it++;
            second_it++;
        }

        return first_it == first.cend() and second_it == second.cend();
    }
};

// map is ordered too, we can iterate like a sequence
#define equal_mapping(TYPE) \
template <typename T, typename U> \
struct access<TYPE<T, U>> \
{ \
    static bool equal_(const TYPE<T, U> & first, const TYPE<T, U> & second) \
    { \
        return first.size() == second.size() && std::equal(first.cbegin(), first.cend(), second.cbegin(), \
            [](decltype(*first.cbegin()) a, decltype(a) b) -> bool { \
                return equal(a, b); \
            } \
        ); \
    } \
};

equal_mapping(std::map);
#undef equal_mapping

#define equal_unorderedmapping(TYPE) \
template <typename T, typename U> \
struct access<TYPE<T, U>> \
{ \
    static bool equal_(const TYPE<T, U> & first, const TYPE<T, U> & second) \
    { \
        if (first.size() != second.size()) \
            return false; \
        \
        auto first_it = first.cbegin(); \
        while (first_it != first.cend()) { \
            auto second_it = second.find(first_it->first); \
            if (second_it == second.cend()) \
                return false; \
            if (not equal(first_it->second, second_it->second)) \
                return false; \
            first_it++; \
        } \
        return true; \
    } \
};

equal_unorderedmapping(std::unordered_map);
#undef equal_unorderedmapping

}
}