Archive::{is_loading,is_saving}::value

[headupinclouds]

Is the following {is_loading,is_saving} type addition compatible with the cereal library? This would greatly improve compatibility with existing boost serialization code and is seemingly unobtrusive.

template<class ArchiveType, std::uint32_t Flags = 0>
  class OutputArchive : public detail::OutputArchiveBase
{
  public:
    typedef bool_<false> is_loading;  // <- proposal
    typedef bool_<true> is_saving;     // <- proposal
   // ...
};

This supports the following serialization pattern:

struct Bar
{
    template <typename Archive> void serialize(Archive &ar, const std::uint32_t version)
    {
        std::int16_t tmp = foo;
        if(Archive::is_loading::value)
        {
            ar & tmp;
            foo = tmp; // For illustration only
        }
        else
        {
            tmp = foo; // For illustration only
            ar & tmp;
        }
        ar & foo;
    }
    std::int32_t foo;
};

[AzothAmmo]

You can actually already get this information by simply using std::is_base_of with the archive and either cereal::detail::InputArchiveBase or cereal::detail::OutputArchiveBase, though I suspect what you are after is identical syntax to boost.

The best place to add this to cereal would be in cereal.hpp to the InputArchive and OutputArchive classes, something along the lines of

using is_loading = std::true_type;
using is_saving  = std::false_type;

as appropriate, defined within the doxygen block for the Boost Transition Layer

If you choose to do a pull request adding this to cereal, please do so against the current develop branch and also include appropriate doxygen comments for the new values.

[headupinclouds]

Thanks for the quick feedback (and a great library). I will put together a PR over the holiday. Having this change upstream will greatly simplify a boost -> cereal transition.

[AzothAmmo]

PR merged.