https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114311
--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
MSVC compiles it but Clang and EDG agree with GCC:
$ clang++ c.cc -std=c++2b
c.cc:12:22: error: non-type template argument is not a constant expression
return SymbolRef<this->id_>{};
^~~~~~~~~
c.cc:12:22: note: use of 'this' pointer is only allowed within the evaluation
of a call to a 'constexpr' member function
c.cc:20:29: error: call to consteval function 'Symbol::operator SymbolRef<1>'
is not a constant expression
static_cast<SymbolRef<1>>(x);
^
c.cc:13:3: note: control reached end of constexpr function
}
^
c.cc:20:29: note: in call to '&x->operator SymbolRef()'
static_cast<SymbolRef<1>>(x);
^
c.cc:20:3: warning: expression result unused [-Wunused-value]
static_cast<SymbolRef<1>>(x);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 warning and 2 errors generated.
$ edg --c++20 c.cc
"c.cc", line 12: error: expression must have a constant value
return SymbolRef<this->id_>{};
^
"c.cc", line 12: note: the value of *this cannot be used as a constant
return SymbolRef<this->id_>{};
^
"c.cc", line 12: error: class "SymbolRef<1>" has no suitable copy constructor
return SymbolRef<this->id_>{};
^
detected during instantiation of "Symbol::operator SymbolRef<Id>()
const [with Id=1]" at line 20
2 errors detected in the compilation of "c.cc".
