Why std::is_same does not work?

My code snippet is:

namespace serialization
{
    struct output_stream
    {
        /////
        void write(const void* data, size_t size)
        {
            const byte_t* p = static_cast<const byte_t*>(data);

            size_t old_size = buffer_.size();
            buffer_.resize(old_size + size);
            memcpy(buffer_.data() + old_size, p, size);
        }
    }

    struct input_stream
    {
        ///////

        void read(void* to, size_t size)
        {
            assert(cur_ + size <= end_);
            memcpy(to, cur_, size);
            cur_ += size;
        }
    }
}

template <class stream_t>
void serialize(not_pod_struct& r, stream_t stream)
{
    if (std::is_same<stream_t, serialization::output_stream>::value)
    {
        stream.write(&r, sizeof(r));
    }
    else if (std::is_same<stream_t, serialization::input_stream>::value)
    {
        not_pod_struct* buf = new not_pod_struct[sizeof(not_pod_struct)];
        stream.read(buf, sizeof(not_pod_struct));
        r = *buf;
    }
    else 
    {
        throw std::invalid_argument("stream_t is not a stream.");
    }
}

template<class T>
typename enable_if<!is_pod<T>::value, void>::type
read(input_stream & input_stream, T & non_pod_struct)
{
    serialize(non_pod_struct, input_stream);
}

template<class T>
typename enable_if<!is_pod<T>::value, void>::type
write(output_stream & output_stream, T & non_pod_struct)
{
    serialize(non_pod_struct, output_stream);
}

I have errors:

Error   1   error C2039: 'read' : is not a member of 'serialization::output_stream'
Error   2   error C2039: 'write' : is not a member of 'serialization::input_stream'

This is strange. I do not understand why these errors happen.