r##"class Foo {
public:
virtual ~Foo() noexcept {}
virtual std::variant<RustString, Error> unpack(std::string_view x) const noexcept = 0;
virtual std::optional<Error> remove() const noexcept = 0;"##;
r#"union CRustVoidOkResultUnion4232mut3232c_void {
uint8_t ok;
void * err;
};"#;