与升压::适配器一起使用boost ::可选::进行间接寻址 [英] Use boost::optional together with boost::adaptors::indirected

问题描述

我试图编译以下code：

I am trying to compile the following code:

#include <iostream>
#include <iterator>
#include <vector>

#include <boost/assign/std/vector.hpp>
#include <boost/optional.hpp>
#include <boost/range/adaptor/indirected.hpp>
#include <boost/range/algorithm/copy.hpp>

int main( int argc, char ** argv )
{
  using namespace boost::assign;
  using boost::adaptors::indirected;

  std::vector<boost::optional<unsigned> > values;
  values += 1u,2u,3u;
  boost::copy( values | indirected, std::ostream_iterator<unsigned>( std::cout, " " ) );
  std::cout << std::endl;
}

不过，我得到了一些错误，例如没有在名为 ELEMENT_TYPE 类型boost ::可选＆LT;无符号＆GT; 。在<一个href=\"http://www.boost.org/doc/libs/1_46_1/libs/range/doc/html/range/reference/adaptors/reference/indirected.html\">reference页面页，但是，说，单precondition是的operator *（）一元函数的存在。有没有一种方法，使工作？

However, I got some errors, e.g. that there is no type named element_type in boost::optional<unsigned>. The reference page page, however, says that the single precondition is the existence of the operator*() unary function. Is there a way to make it work?

推荐答案

这绝对是一个升压错误，但错误是否在Boost.Optional或Boost.Iterator是为辩论（我会说后者，亲自）。

This is definitely a bug in Boost, but whether that bug is in Boost.Optional or Boost.Iterator is up for debate (I would say the latter, personally).

不过，解决方法是微不足道的 - 包括任何Boost头文件之前，这样做：

However, the fix is trivial -- before including any Boost headers, do this:

#include <boost/optional/optional_fwd.hpp>
#include <boost/pointee.hpp>

namespace boost
{
    template<typename P>
    struct pointee<optional<P> >
    {
        typedef typename optional<P>::value_type type;
    };
}

然后包括其他Boost头文件是必要的。

Then include other Boost headers as necessary.

请在提升Trac的，或至少发布一个bug报告在提升用户邮件列表。

Please submit a ticket on the Boost Trac, or at the least post a bug report on the Boost Users mailing list.

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