C++20/23 std::string implementation

Single-header, almost fully complete C++20/23 std::string implementation with sso support.
Can be used in a freestanding environment with https://github.com/ilobilo/libstdcxx-headers and custom header <memory> that implements std::allocator<>.
See memory for the reference implementation.

Note: This header has not been fully tested. if there are any compilation errors or some methods don't function as C++ standard states, please open a github issue.

Including

• You can use this header by adding include to your headers search path:
  -I$(this_dir)/include
• If you use meson, you can also do:
  dependency('string')

Supported options

• NOSTD_STRING_NUMERIC_CONVERSIONS: Enable support for numeric conversion functions.
• NOSTD_STRING_FLOAT: Enable floating point numeric conversion functions.
• NOSTD_STRING_LONG_DOUBLE: Enable support for long double in numeric conversion functions. (Needs NOSTD_STRING_FLOAT)
• NOSTD_STRING_EXCEPTIONS: Enable exceptions support.
• NOSTD_STRING_FALLBACK_ASSERT: Use assert() from <cassert> if exceptions are not available.
• NOSTD_STRING_FALLBACK_ABORT Use std::abort() from <cstdlib> if nether exceptions nor assert() is available.
• NOSTD_STRING_FALLBACK_ABORT_FUNCTION: Function to run and then loop indefinitely, if nether exceptions, assert() nor std::abort() is available. (Default value: [] (auto) { }. Function takes error string literal as an argument)
• NOSTD_STRING_STD_HASH: Enable support for std::hash. (Uses Murmurhash2-64a)
• NOSTD_STRING_CONTAINERS_RANGES: Enable support for C++23 P1206R4: Conversions from ranges to containers.

Note: Every option is enabled by default.
Note: Every option apart from NOSTD_STRING_STD_HASH will be automatically disabled if required headers or functions were not found or option that they depend on is not enabled.

Example usage

#include <nostd/string.hpp>
#include <iostream> // for std::cout

// currently constexpr string must fit in sso
// alternatively you can use std::string_view
constexpr nostd::string world("World");

auto main() -> int
{
    using namespace nostd::literals::string_literals;
    auto hello = "Hello"s;

    nostd::string str = hello + ", " + world + "!";

    // you could also overload std::cout to support nostd::string
    std::cout << str.c_str() << std::endl;
    return 0;
}

Output:

Hello, World!

Currently missing functions:

• resize_and_overwrite
• to_string(float/double/long double)
• to_wstring(all)