In a constexpr function, I am unable to define a non-literal variable within the branch of an if statement conditioned by C++20's std::is_constant_evaluated()? Clang and GCC both indicate it is not permitted, but in the example below, other constructs which cannot be evaluated at compile-time are permitted. Is there a specific restriction on the use of non-literals?
#include <type_traits> struct Foo { ~Foo() {} }; void non_constexpr() {} constexpr bool bar() { if (std::is_constant_evaluated()) { } else { non_constexpr(); double d; reinterpret_cast<int*>(&d); Foo f; // error: variable ‘f’ of non-literal type ‘Foo’ in ‘constexpr’ function } return true; } constexpr bool x = bar(); 
