C++ How to call the methods of a template variadic type list inside a method of the class which derived from that list?

Question

So I want a class which allows a sequence of classes to call their decode/encode methods in that way:

/// This class manages the decoding/encoding of a sequence of binary fields.
template <typename Derived, typename... Fields >
struct BinarySequence : Fields...
{
    using Super = BinarySequence;

    bool decode(const char* buffer, size_t& length)
    {
        return true && Fields...::decode(buffer, length);
    }

    bool encode(char* buffer, size_t& length)
    {
        return true && Fields...::encode(buffer, length);
    }
};

The issue is to call Fields...::decode(buffer, length) is not the correct way. If I have BinarySequence< MessageType, MessageSender, MessageTimeStamp >, I want its decoder to do the same as

bool decode(const char* buffer, size_t& length)
{
    return MessageType::decode(buffer, length) && MessageSender::decode(buffer, length) && MessageTimeStamp::decode(buffer, length);
}

What would be the right way to do so? I use Visual Studio Code 2017.

Answer 1

Have a look at fold expressions. The correct syntax is:

/// This class manages the decoding/encoding of a sequence of binary fields.
template <typename Derived, typename... Fields >
struct BinarySequence : Fields...
{
    using Super = BinarySequence;

    bool decode(const char* buffer, size_t& length)
    {
        return (Fields::decode(buffer, length) && ...);
    }

    bool encode(char* buffer, size_t& length)
    {
        return (Fields::encode(buffer, length) && ...);
    }
};

This requires C++17 or newer.