CompileTimeType: force compiler to show you inferred types

CompileTimeType.cc

// See: EMC++, Item 4
template<typename>
class CompileTimeType;

int main() {
  int x;


  CompileTimeType<decltype(x)> x_Type;

  // cttype.cc:7:32: error: implicit instantiation of undefined template 'CompileTimeType<int>'
  //   CompileTimeType<decltype(x)> x_Type;                                              ^^^^^


  CompileTimeType<decltype((x))> xb_Type;

  // cttype.cc:8:34: error: implicit instantiation of undefined template 'CompileTimeType<int &>'
  //   CompileTimeType<decltype((x))> xb_Type;                                           ^^^^^^^
}