我想做以下事情:
std::vector<int> a = {1,2,3}, b = {4,5,6}, c = {7,8,9};
for(auto&& i : join(a,b,c)) {
i += 1
std::cout << i; // -> 2345678910
}
我尝试使用boost::range::join
,这很好用:
auto r = boost::join(a,b);
for(auto&& i : boost::join(r,c)) {
i += 1;
std::cout << i; // -> 2345678910
}
链接连接,读取操作工作:
for(auto&& i : boost::join(boost::join(a,b),c))
std::cout << i; // -> 123456789
但是,写作不起作用:
for(auto&& i : boost::join(boost::join(a,b),c)) {
i += 1; // Fails :(
std::cout << i;
}
我的可变连接有同样的问题,即适用于阅读但不适用于写作:
template<class C> C&& join(C&& c) { return c; }
template<class C, class D, class... Args>
auto join(C&& c, D&& d, Args&&... args)
-> decltype(boost::join(boost::join(std::forward<C>(c), std::forward<D>(d)),
join(std::forward<Args>(args)...))) {
return boost::join(boost::join(std::forward<C>(c), std::forward<D>(d)),
join(std::forward<Args>(args)...));
}
Mehrdad 在评论中给出了解决方案
template<class C>
auto join(C&& c)
-> decltype(boost::make_iterator_range(std::begin(c),std::end(c))) {
return boost::make_iterator_range(std::begin(c),std::end(c));
}
template<class C, class D, class... Args>
auto join(C&& c, D&& d, Args&&... args)
-> decltype(boost::join(boost::join(boost::make_iterator_range(std::begin(c),std::end(c)),
boost::make_iterator_range(std::begin(d),std::end(d))),
join(std::forward<Args>(args)...))) {
return boost::join(boost::join(boost::make_iterator_range(std::begin(c),std::end(c)),
boost::make_iterator_range(std::begin(d),std::end(d))),
join(std::forward<Args>(args)...));
}