- everything should ideally be constexpr. The problem here is that
constexpr requires initializing all elements, and this will heavily
penalize runtime uses of f.ex. fixed_string<512>. On compilers with
__builtin_is_constant_evaluated (gcc 9, clang 9) we should use that;
otherwise, it might be worth it to create a specialization for N < some
suitable upper limit.
Wait, I have an idea.
template struct fixed_string
{
private:
std::size_t size_ = 0;
union
{
char first_ = 0;
char data_[ N+1 ];
};
public:
fixed_string() = default;
};
Now default initialization sets just the first char to zero, as we want, and
value initialization initializes all data_ to zero and is constexpr.
auto f1()
{
fixed_string<24> s;
return s;
}
auto f2()
{
constexpr fixed_string<24> s{};
return s;
}
https://godbolt.org/z/uhf4S4
I don't know if that's defined behavior or not, but if it isn't, it better
be.
