Take this (working) program https://godbolt.org/z/rY3hh8boG It creates a type, which remembers both types, int and double and its value: So it does, what you propose. However, it wraps the feature into a new type. auto var = make_auto<double>(); var.printTypes(); // prints double and int cout << typeid(var).name() << endl; cout << var << endl; int var2 = var; cout << var2 << endl; d -> double i -> int 11AutoWrapperIdiE -> AutoWrapper<double, int> 123 -> value 123 -> value Why should this be implicitly done with existing types instead? Lots of C++ depends on knowing the exact type. By making two types, which were the same before suddenly different, existing code breaks. E.g. static variables in templated functions would exist independently, where before they were shared.