rsl::kwargs is an experimental single-header library that allows for keyword arguments (also known as labeled or named arguments) through use of C++26 reflection (P2996).
You can find more information about it's implementation in my blog post Fun with C++26 reflection - Keyword Arguments.
This is a single-header library, to use it simply copy kwargs.h into your project's source tree.
In order to use this library, you need a compiler with P2996 reflection support. Currently only Bloomberg's experimental clang fork is supported, it's completely untested with EDG's implementation. If you require support for that, please reach out to me (ie via issue, email or discord). PRs are also welcome.
Compile with -freflection and compile and link against libc++ instead of libstdc++ (otherwise <experimental/meta> will not be found).
You can opt into wrappers around std::print, std::println and std::format with support for named arguments by defining KWARGS_FORMATTING=1.
#include <print>
#define KWARGS_FORMATTING 1
#include <kwargs.h>
template <typename T>
int test(int x, rsl::kwargs_t<T> args){
return x * get<"y">(args, 42);
}
int main(){
std::println("test({}, {}) -> {}", 7, "y=42",
test(7, make_args(y=23)));
std::println("test({}, {}) -> {}", 7, "z=42",
test(7, make_args(z=23)));
// optional wrappers around `std::format`, `std::println`
// and `std::format`
int y = 3;
rsl::println("foo: {foo} bar: {bar}",
make_args(bar=3,
foo=test(7, make_args(y))));
}Can be compiled and executed from this project's root by invoking
mkdir -p build
clang++ -std=c++26 -freflection -stdlib=libc++ -Iinclude example/simple.cpp -o build/simple
./build/simpleMore examples can be found in the example subdirectory of this repository.
kwargs is provided under the MIT License. Feel free to use and modify it in your projects.