foo.cc:2:20: error: expected ‘;’ before ‘(’ token
    2 | using namespace std()
      |                    ^
      |                    ;
foo.cc:2:21: error: expected unqualified-id before ‘)’ token
    2 | using namespace std()
      |                     ^
foo.cc:4:1: error: expected unqualified-id before ‘{’ token
    4 | {
      | ^