【C++11】 Designated Initializer 風な何か Boost.Fusion 対応

はい、という訳で当初目標であった、Designated Initializer 風な何かの Boost.Fusion 対応ができました。実際のコードは https://github.com/yak1ex/cpp_stuff にあります。GCC 4.7 専用です。書いた後で言うのもなんですが、まぁ余程でかい構造体でなければ全部初期化子書いた方が早いだろ、という気はします。あと最初っからやる気があるなら Boost.Parameter 使えばいいんじゃね？、みたいな。配列の場合は意味があるケースはあるかもしれません。特定の添字だけじゃなくて range<5, 12>() = 1 と書くと 5 ～ 11 が 1 で初期化とかだとより意味があるケースが出てくるかも。

テストコード

#include <vector>
#include <iostream>

#include <boost/fusion/include/adapt_struct.hpp>
#include <boost/fusion/include/define_struct.hpp>
#include <boost/array.hpp>
#include <boost/fusion/include/boost_array.hpp>
#include <boost/tuple/tuple.hpp>
#include <boost/fusion/include/boost_tuple.hpp>
#include <boost/fusion/include/adapt_assoc_struct.hpp>

#include <boost/fusion/include/out.hpp>

#include "dinit.hpp"

// Helper function

template<typename T>
void output(const T& v)
{
 for(auto val : v) {
  std::cout << ' ' << val;
 }
 std::cout << std::endl;
}

// Type definition and adapter

// Don't work for BOOST_FUSION_DEFINE_STRUCT becaues conflict with constructor

struct employee
{
 std::string name;
 int age;
 double rate;
};

BOOST_FUSION_ADAPT_STRUCT(
 employee,
 (std::string, name)
 (int, age)
 (double, rate)
)

namespace keys {
 struct name;
 struct age;
 struct rate;
}

struct employee_
{
 std::string name;
 int age;
 double rate;
};


BOOST_FUSION_ADAPT_ASSOC_STRUCT(
 employee_,
 (std::string, name, keys::name)
 (int, age, keys::age)
 (double, rate, keys::rate)
)

// Don't work for plain array because brace-enclosed initializer is required.

int main(void)
{
 using yak::util::dinit::di;
 using yak::util::dinit::idx;
 using yak::util::dinit::idx_;
 using yak::util::dinit::key;
 using yak::util::dinit::key_;

// For sequence with list constructor

 std::vector<int> v = di(idx<10>() = 1, idx<0>() = 2, idx<2>() = 3, idx<3>() = 4);
 output(v);

 std::vector<int> v2 = di(idx_<10>(1), idx_<0>(2), idx_<2>(3), idx_<3>(4));
 output(v2);

// For Fusion sequence with idx

 employee e = di(idx<2>() = 3.3, idx<1>() = 33);
 boost::fusion::out(std::cout, e); std::cout << std::endl;

 boost::array<int, 5> ar2 = di(idx<3>() = 4);
 output(ar2);

 boost::tuple<std::string, int, double> t = di(idx<1>() = 5);
 boost::fusion::out(std::cout, t); std::cout << std::endl;

// For Fusion sequence with tag

 employee_ e2 = di(key<keys::rate>() = 3.3, key<keys::age>() = 33);
 boost::fusion::out(std::cout, e2); std::cout << std::endl;

 employee_ e3 = di(key_<keys::rate>(3.3), key_<keys::age>(33));
 boost::fusion::out(std::cout, e3); std::cout << std::endl;

 return 0;
}

出力

 2 0 3 4 0 0 0 0 0 0 1
 2 0 3 4 0 0 0 0 0 0 1
( 33 3.3)
 0 0 0 4 0
( 5 0)
( 33 3.3)
( 33 3.3)