Boost.Fit Review Samples

main1.cpp

#include <boost/fit/fold.hpp>
#include <boost/fit/alias.hpp>
#include <iostream>
#include <string>

namespace fit = boost::fit;


struct my_string_tag { };
using my_string = fit::alias_inherit<std::string, my_string_tag>;

constexpr auto plus = [](auto const& x, auto const& y) { return x + y; };
constexpr auto sum = fit::fold(plus);

int main()
{
  my_string result = sum(
    my_string("Hello")
  , my_string(", ")
  , my_string("world!")
  );
  std::cout << result << '\n';
}

main2.cpp

#include <boost/fit/alias.hpp>
#include <boost/fit/arg.hpp>
#include <boost/fit/by.hpp>
#include <boost/fit/decay.hpp>
#include <boost/fit/partial.hpp>
#include <boost/fit/returns.hpp>
#include <iostream>
#include <vector>

namespace fit = boost::fit;


struct my_int_tag { };
using my_int = fit::alias<int, my_int_tag>;

constexpr auto make_vector = [](auto&& ...x) BOOST_FIT_RETURNS(
  std::vector<decltype(fit::decay(fit::arg_c<1>(x...)))>{
    x...
  }
);

constexpr auto transform_in_place = [](auto const& f, auto& x)
{ return std::transform(x.begin(), x.end(), x.begin(), f); };

constexpr auto inc = [](auto x) -> decltype(x) { return fit::alias_value(x) + 1; };
constexpr auto inc_all = fit::partial(transform_in_place)(inc);

int main()
{
  auto nums = make_vector(
    my_int{0}
  , my_int{1}
  , my_int{2}
  , my_int{3}
  );

  inc_all(nums);

  for (auto const& x : nums)
  {
    std::cout << fit::alias_value(x) << '\n';
  }
}