View Compilation Error

0_0_36839569_31064.cpp: In static member function 'static constexpr mat mat::e()':
0_0_36839569_31064.cpp:12:50: error: could not convert '{{{{1, 0}, {0, 1}}}}' from '<brace-enclosed initializer list>' to 'mat'
  static constexpr mat e(){return {{{{1,0},{0,1}}}};}
                                                  ^
0_0_36839569_31064.cpp:12:52: error: body of constexpr function 'static constexpr mat mat::e()' not a return-statement
  static constexpr mat e(){return {{{{1,0},{0,1}}}};}
                                                    ^