The problem with this argument is that user-defined literals already exist in C++11, and use of the underscore character for a different purpose in a future sta

The problem with this argument is that user-defined literals already exist in C++11, and use of the underscore character for a different purpose in a future standard has to be in such a way that it can be unambiguously distinguished from the user-defined literal usage. Backward-compatibility to the current standard has to be preserved.