Linux, Clang:

/home/buildbot/worker/l-upphub-StreamCypher/build/StreamCypher/examples/StreamCypherTest/StreamCypherTest.cpp:85:9: error: definition or redeclaration of 'String' not allowed inside a function
                Snow2 S(key);
                      ^~~~~~
/home/buildbot/worker/l-upphub-StreamCypher/build/Functions4U/Functions4U/Functions4U.h:1013:19: note: expanded from macro 'S'
#define S(y)    Upp::String(y)
                ~~~~~^
/home/buildbot/worker/l-upphub-StreamCypher/build/StreamCypher/examples/StreamCypherTest/StreamCypherTest.cpp:85:9: error: no member named 'String' in namespace 'Upp'
                Snow2 S(key);
                      ^~~~~~
/home/buildbot/worker/l-upphub-StreamCypher/build/Functions4U/Functions4U/Functions4U.h:1013:19: note: expanded from macro 'S'
#define S(y)    Upp::String(y)
                ~~~~~^
/home/buildbot/worker/l-upphub-StreamCypher/build/StreamCypher/examples/StreamCypherTest/StreamCypherTest.cpp:89:8: error: use of undeclared identifier 'S'
                        d = S.Encode(s);
                            ^
/home/buildbot/worker/l-upphub-StreamCypher/build/StreamCypher/examples/StreamCypherTest/StreamCypherTest.cpp:99:5: error: must use 'class' tag to refer to type 'String' in this scope
                                String ss = s.Left(rnd);
                                ^
                                class 
/home/buildbot/worker/l-upphub-StreamCypher/build/StreamCypher/examples/StreamCypherTest/StreamCypherTest.cpp:85:9: note: class 'String' is hidden by a non-type declaration of 'String' here
                Snow2 S(key);
                      ^
/home/buildbot/worker/l-upphub-StreamCypher/build/Functions4U/Functions4U/Functions4U.h:1013:19: note: expanded from macro 'S'
#define S(y)    Upp::String(y)
                     ^
/home/buildbot/worker/l-upphub-StreamCypher/build/StreamCypher/examples/StreamCypherTest/StreamCypherTest.cpp:102:10: error: use of undeclared identifier 'S'
                                d += S.Encode(ss);
                                     ^