Error(s):

236020889/source.cpp:11:30: error: constexpr variable 'diff' must be initialized by a constant expression
    constexpr std::ptrdiff_t diff = p10 - p00;
                             ^      ~~~~~~~~~
236020889/source.cpp:11:41: note: subtracted pointers are not elements of the same array
    constexpr std::ptrdiff_t diff = p10 - p00;
                                        ^
1 error generated.