reference operator[](size_type i) noexcept { return *skeletons[i]; }
const_reference operator[](size_type i) const noexcept { return *skeletons[i]; }
reference operator[](size_type i) noexcept { return *skeletons[i]; }
const_reference operator[](size_type i) const noexcept { return *skeletons[i]; }