There is a set list of allowable types for user-defined literals in the C++ standard:
https://en.cppreference.com/w/cpp/language/user_literal.html
We do not reject these by default upon declaration, and the way in which we currently reject them is at point-of-use when we say that we cannot find a match for a "literal suffix".
There is a set list of allowable types for user-defined literals in the C++ standard:
https://en.cppreference.com/w/cpp/language/user_literal.html
We do not reject these by default upon declaration, and the way in which we currently reject them is at point-of-use when we say that we cannot find a match for a "literal suffix".