Json::m_ptr looks like std::unique_ptr would be more suited

[Amleto]

Json::m_ptr looks like std::unique_ptr would be more suited? I didn't see any sharing that suggests shared_ptr is needed, but only eye-balled it.

[j4cbo]

The implicit copy constructor of Json will copy the shared_ptr, thus making a shallow copy of the object (increasing the refcount). This is safe since the underlying objects are immutable; the intention was to make Json a lightweight handle-like type.