A C++17 (with GNU extensions) header-only named arguments library based on an idea from Richard Powell presented on CppCon 2018 “Named Arguments from Scratch”.

https://youtu.be/Grveezn0zhU

• Boost Hana

• GCC 8
• clang 7

Example:

#include <named_arguments.hpp>

#include <string>
#include <iostream>


using namespace named_arguments::literals;


float foo(int a, float&& b, std::string const& c){
    return a + b * c.size();
};


auto bar = named_arguments::adapt(
    foo,
    "a"_default_arg = []{ return 10; },
    "b"_no_default_arg,
    "c"_default_arg = []{ return "string"; });


int main(){
    auto v = bar("c"_arg = "string", "b"_arg = 0.5f);
    std::cout << v << '\n';
}

Use named_arguments::literals to import 3 user defined literals: "param_name"_default_arg, "param_name"_no_default_arg and "param_name"_arg.

Then you need a callable foo that you wrap into a new callable bar by named_arguments::adapt. The adapt call maps the parameters from its original call order to some parameter names. You can use "param_name"_no_default_arg if you just want to specify a name for the parameter or "param_name"_default_arg if you also want to set a default value. Default values must be specified by another callable without parameters! Most likly a lambda as in the example. This way the default value dosn't need to be copy- or movable. You must map all parameters, only a subset is invalid.

Then you can call bar by assign the values to its names. The names in a call must be declared with "param_name"_arg.

All parameters and the return value are perfect forwareded.

float v;
bar("b"_arg = std::move(v));

To build the unit tests you need CMake 3.12.4.

Build and exec tests with:

cd test
mkdir build
cd build
cmake ..
make
./simple_wrap

This software was originally developed privately by Benjamin Buch. All changes are released under the Boost Software License - Version 1.0 and published on GitHub.

https://github.com/bebuch/named-arguments