View Compilation Error

0_0_26278450_18542.cpp:52:16: error: enclosing class of constexpr non-static member function 'int Graph::__foo(int) const' is not a literal type
  constexpr int __foo(int v){
                ^
0_0_26278450_18542.cpp:6:7: note: 'Graph' is not literal because:
 class Graph{
       ^
0_0_26278450_18542.cpp:6:7: note:   'Graph' has a non-trivial destructor
0_0_26278450_18542.cpp: In constructor 'Graph::Graph(int)':
0_0_26278450_18542.cpp:14:56: error: invalid types '<unresolved overloaded function type>[int]' for array subscript
   for(auto i = 0; i < foo.size(); ++i) foo[i] = __foo[i];
                                                        ^