https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105050
Jonathan Wakely <redi at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Last reconfirmed| |2022-03-25 Ever confirmed|0 |1 Status|UNCONFIRMED |NEW --- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> --- If it just said that the body of swap(expected&) was not a constant expression, that would have been an improvement. I spent ages trying to understand what was wrong with this line: x.ii:15:7: error: expression '<statement>' is not a constant expression 15 | if (this->has_value()) | ^~ In fact the `if` statements are the only ones in the function that *are* constant expressions, the problem is all the *other* statements. All the return statements have non-constant operands.