C++20 will add constexpr strings and vectors
The following proposal has been accepted apparently: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0980r0.pdf and it adds constructors such as:
// 20.3.2.2, construct/copy/destroy
constexpr
basic_string() noexcept(noexcept(Allocator())) : basic_string(Allocator()) { }
constexpr
explicit basic_string(const Allocator& a) noexcept;
constexpr
basic_string(const basic_string& str);
constexpr
basic_string(basic_string&& str) noexcept;
in addition to constexpr versions of all / most methods.
There is no support as of GCC 9.1.0, the following fails to compile:
#include <string>
int main() {
constexpr std::string s("abc");
}
with:
g++-9 -std=c++2a main.cpp
with error:
error: the type ‘const string’ {aka ‘const std::__cxx11::basic_string<char>’} of ‘constexpr’ variable ‘s’ is not literal
std::vector discussed at: Cannot create constexpr std::vector
Tested in Ubuntu 19.04.