通常 std::bind 是否适用于仅移动类型，特别是 std::unique_ptr ？答案

【问题标题】：Does std::bind work with move-only types in general, and std::unique_ptr in particular?通常 std::bind 是否适用于仅移动类型，特别是 std::unique_ptr ？
【发布时间】：2012-04-14 21:22:29
【问题描述】：

我正在尝试使用 boost::asio 并遇到了一些泥潭。

我正在尝试编译以下代码：

std::unique_ptr<buffer_t> buffer = buffers.pop();
std::function<void(const boost::system::error_code&, size_t)> t = std::bind(&tcp_client::handle_read_done,
                                                                            this,
                                                                            std::placeholders::_1,
                                                                            std::placeholders::_2,
                                                                            std::move(buffer));

如果我将 std::move(buffer) 排除在外，一切正常，当然，这既来自 handle_read_done 的签名，也作为 std::bind 中的传递参数。

当试图将它传递给 boost::asio::async_read_some 时，它抱怨从 std::bind 返回的对象上隐式删除的函数，元组上的已删除函数，我认为这是因为可移动性，以及很多提升特定的错误。如果我只是尝试将它分配到一个应该与 boost 调用的签名匹配的 std::function 中，我会得到相同的元组错误，所以我猜它们是相同的。只需将 std::bind 的结果分配给 auto 不会产生编译器错误，但我当然不能在其上调用任何东西。

我做错了什么？以下是尝试分配给std::function<void(const boost::system::error_code&,size_t)> 时的输出

/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/functional: In static member function ‘static void std::_Function_handler<void(_ArgTypes ...), _Functor>::_M_invoke(const std::_Any_data&, _ArgTypes ...) [with _Functor = std::_Bind<std::_Mem_fn<void (rcon::net::tcp_client::*)(const boost::system::error_code&, long unsigned int, std::unique_ptr<std::array<unsigned char, 10240ul> >)>(rcon::net::tcp_client*, std::_Placeholder<1>, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> >)>, _ArgTypes = {const boost::system::error_code&, long unsigned int}]’:
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/functional:2148:6:   instantiated from ‘std::function<_Res(_ArgTypes ...)>::function(_Functor, typename std::enable_if<(! std::is_integral<_Functor>::value), std::function<_Res(_ArgTypes ...)>::_Useless>::type) [with _Functor = std::_Bind<std::_Mem_fn<void (rcon::net::tcp_client::*)(const boost::system::error_code&, long unsigned int, std::unique_ptr<std::array<unsigned char, 10240ul> >)>(rcon::net::tcp_client*, std::_Placeholder<1>, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> >)>, _Res = void, _ArgTypes = {const boost::system::error_code&, long unsigned int}, typename std::enable_if<(! std::is_integral<_Functor>::value), std::function<_Res(_ArgTypes ...)>::_Useless>::type = std::function<void(const boost::system::error_code&, long unsigned int)>::_Useless]’
/home/max/dev/rcon/src/net/tcp_client.cpp:98:34:   instantiated from here
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/functional:1778:2: error: no match for call to ‘(std::_Bind<std::_Mem_fn<void (rcon::net::tcp_client::*)(const boost::system::error_code&, long unsigned int, std::unique_ptr<std::array<unsigned char, 10240ul> >)>(rcon::net::tcp_client*, std::_Placeholder<1>, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> >)>) (const boost::system::error_code&, long unsigned int)’
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/functional:1130:11: note: candidates are:
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/functional:1201:2: note: template<class ... _Args, class _Result> _Result std::_Bind<_Functor(_Bound_args ...)>::operator()(_Args&& ...) [with _Args = {_Args ...}, _Result = _Result, _Functor = std::_Mem_fn<void (rcon::net::tcp_client::*)(const boost::system::error_code&, long unsigned int, std::unique_ptr<std::array<unsigned char, 10240ul> >)>, _Bound_args = {rcon::net::tcp_client*, std::_Placeholder<1>, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> >}]
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/functional:1215:2: note: template<class ... _Args, class _Result> _Result std::_Bind<_Functor(_Bound_args ...)>::operator()(_Args&& ...) const [with _Args = {_Args ...}, _Result = _Result, _Functor = std::_Mem_fn<void (rcon::net::tcp_client::*)(const boost::system::error_code&, long unsigned int, std::unique_ptr<std::array<unsigned char, 10240ul> >)>, _Bound_args = {rcon::net::tcp_client*, std::_Placeholder<1>, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> >}]
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/functional:1229:2: note: template<class ... _Args, class _Result> _Result std::_Bind<_Functor(_Bound_args ...)>::operator()(_Args&& ...) volatile [with _Args = {_Args ...}, _Result = _Result, _Functor = std::_Mem_fn<void (rcon::net::tcp_client::*)(const boost::system::error_code&, long unsigned int, std::unique_ptr<std::array<unsigned char, 10240ul> >)>, _Bound_args = {rcon::net::tcp_client*, std::_Placeholder<1>, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> >}]
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/functional:1243:2: note: template<class ... _Args, class _Result> _Result std::_Bind<_Functor(_Bound_args ...)>::operator()(_Args&& ...) const volatile [with _Args = {_Args ...}, _Result = _Result, _Functor = std::_Mem_fn<void (rcon::net::tcp_client::*)(const boost::system::error_code&, long unsigned int, std::unique_ptr<std::array<unsigned char, 10240ul> >)>, _Bound_args = {rcon::net::tcp_client*, std::_Placeholder<1>, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> >}]
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/functional: In static member function ‘static void std::_Function_base::_Base_manager<_Functor>::_M_clone(std::_Any_data&, const std::_Any_data&, std::false_type) [with _Functor = std::_Bind<std::_Mem_fn<void (rcon::net::tcp_client::*)(const boost::system::error_code&, long unsigned int, std::unique_ptr<std::array<unsigned char, 10240ul> >)>(rcon::net::tcp_client*, std::_Placeholder<1>, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> >)>, std::false_type = std::integral_constant<bool, false>]’:
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/functional:1652:8:   instantiated from ‘static bool std::_Function_base::_Base_manager<_Functor>::_M_manager(std::_Any_data&, const std::_Any_data&, std::_Manager_operation) [with _Functor = std::_Bind<std::_Mem_fn<void (rcon::net::tcp_client::*)(const boost::system::error_code&, long unsigned int, std::unique_ptr<std::array<unsigned char, 10240ul> >)>(rcon::net::tcp_client*, std::_Placeholder<1>, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> >)>]’
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/functional:2149:6:   instantiated from ‘std::function<_Res(_ArgTypes ...)>::function(_Functor, typename std::enable_if<(! std::is_integral<_Functor>::value), std::function<_Res(_ArgTypes ...)>::_Useless>::type) [with _Functor = std::_Bind<std::_Mem_fn<void (rcon::net::tcp_client::*)(const boost::system::error_code&, long unsigned int, std::unique_ptr<std::array<unsigned char, 10240ul> >)>(rcon::net::tcp_client*, std::_Placeholder<1>, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> >)>, _Res = void, _ArgTypes = {const boost::system::error_code&, long unsigned int}, typename std::enable_if<(! std::is_integral<_Functor>::value), std::function<_Res(_ArgTypes ...)>::_Useless>::type = std::function<void(const boost::system::error_code&, long unsigned int)>::_Useless]’
/home/max/dev/rcon/src/net/tcp_client.cpp:98:34:   instantiated from here
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/functional:1616:4: error: use of deleted function ‘std::_Bind<_Functor(_Bound_args ...)>::_Bind(const std::_Bind<_Functor(_Bound_args ...)>&) [with _Functor = std::_Mem_fn<void (rcon::net::tcp_client::*)(const boost::system::error_code&, long unsigned int, std::unique_ptr<std::array<unsigned char, 10240ul> >)>, _Bound_args = {rcon::net::tcp_client*, std::_Placeholder<1>, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> >}, std::_Bind<_Functor(_Bound_args ...)> = std::_Bind<std::_Mem_fn<void (rcon::net::tcp_client::*)(const boost::system::error_code&, long unsigned int, std::unique_ptr<std::array<unsigned char, 10240ul> >)>(rcon::net::tcp_client*, std::_Placeholder<1>, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> >)>]’
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/functional:1189:7: error: ‘std::_Bind<_Functor(_Bound_args ...)>::_Bind(const std::_Bind<_Functor(_Bound_args ...)>&) [with _Functor = std::_Mem_fn<void (rcon::net::tcp_client::*)(const boost::system::error_code&, long unsigned int, std::unique_ptr<std::array<unsigned char, 10240ul> >)>, _Bound_args = {rcon::net::tcp_client*, std::_Placeholder<1>, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> >}, std::_Bind<_Functor(_Bound_args ...)> = std::_Bind<std::_Mem_fn<void (rcon::net::tcp_client::*)(const boost::system::error_code&, long unsigned int, std::unique_ptr<std::array<unsigned char, 10240ul> >)>(rcon::net::tcp_client*, std::_Placeholder<1>, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> >)>]’ is implicitly deleted because the default definition would be ill-formed:
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/functional:1189:7: error: use of deleted function ‘constexpr std::tuple< <template-parameter-1-1> >::tuple(const std::tuple< <template-parameter-1-1> >&) [with _Elements = {rcon::net::tcp_client*, std::_Placeholder<1>, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> >}, std::tuple< <template-parameter-1-1> > = std::tuple<rcon::net::tcp_client*, std::_Placeholder<1>, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> > >]’
In file included from /usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/functional:56:0,
                 from /home/max/dev/rcon/include/net/tcp_client.hpp:4,
                 from /home/max/dev/rcon/src/net/tcp_client.cpp:1:
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/tuple:249:17: error: ‘constexpr std::tuple< <template-parameter-1-1> >::tuple(const std::tuple< <template-parameter-1-1> >&) [with _Elements = {rcon::net::tcp_client*, std::_Placeholder<1>, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> >}, std::tuple< <template-parameter-1-1> > = std::tuple<rcon::net::tcp_client*, std::_Placeholder<1>, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> > >]’ is implicitly deleted because the default definition would be ill-formed:
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/tuple:249:17: error: use of deleted function ‘constexpr std::_Tuple_impl<_Idx, _Head, _Tail ...>::_Tuple_impl(const std::_Tuple_impl<_Idx, _Head, _Tail ...>&) [with long unsigned int _Idx = 0ul, _Head = rcon::net::tcp_client*, _Tail = {std::_Placeholder<1>, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> >}, std::_Tuple_impl<_Idx, _Head, _Tail ...> = std::_Tuple_impl<0ul, rcon::net::tcp_client*, std::_Placeholder<1>, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> > >]’
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/tuple:170:17: error: ‘constexpr std::_Tuple_impl<_Idx, _Head, _Tail ...>::_Tuple_impl(const std::_Tuple_impl<_Idx, _Head, _Tail ...>&) [with long unsigned int _Idx = 0ul, _Head = rcon::net::tcp_client*, _Tail = {std::_Placeholder<1>, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> >}, std::_Tuple_impl<_Idx, _Head, _Tail ...> = std::_Tuple_impl<0ul, rcon::net::tcp_client*, std::_Placeholder<1>, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> > >]’ is implicitly deleted because the default definition would be ill-formed:
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/tuple:170:17: error: use of deleted function ‘constexpr std::_Tuple_impl<_Idx, _Head, _Tail ...>::_Tuple_impl(const std::_Tuple_impl<_Idx, _Head, _Tail ...>&) [with long unsigned int _Idx = 1ul, _Head = std::_Placeholder<1>, _Tail = {std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> >}, std::_Tuple_impl<_Idx, _Head, _Tail ...> = std::_Tuple_impl<1ul, std::_Placeholder<1>, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> > >]’
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/tuple:170:17: error: ‘constexpr std::_Tuple_impl<_Idx, _Head, _Tail ...>::_Tuple_impl(const std::_Tuple_impl<_Idx, _Head, _Tail ...>&) [with long unsigned int _Idx = 1ul, _Head = std::_Placeholder<1>, _Tail = {std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> >}, std::_Tuple_impl<_Idx, _Head, _Tail ...> = std::_Tuple_impl<1ul, std::_Placeholder<1>, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> > >]’ is implicitly deleted because the default definition would be ill-formed:
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/tuple:170:17: error: use of deleted function ‘constexpr std::_Tuple_impl<_Idx, _Head, _Tail ...>::_Tuple_impl(const std::_Tuple_impl<_Idx, _Head, _Tail ...>&) [with long unsigned int _Idx = 2ul, _Head = std::_Placeholder<2>, _Tail = {std::unique_ptr<std::array<unsigned char, 10240ul> >}, std::_Tuple_impl<_Idx, _Head, _Tail ...> = std::_Tuple_impl<2ul, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> > >]’
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/tuple:170:17: error: ‘constexpr std::_Tuple_impl<_Idx, _Head, _Tail ...>::_Tuple_impl(const std::_Tuple_impl<_Idx, _Head, _Tail ...>&) [with long unsigned int _Idx = 2ul, _Head = std::_Placeholder<2>, _Tail = {std::unique_ptr<std::array<unsigned char, 10240ul> >}, std::_Tuple_impl<_Idx, _Head, _Tail ...> = std::_Tuple_impl<2ul, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> > >]’ is implicitly deleted because the default definition would be ill-formed:
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/tuple:170:17: error: use of deleted function ‘constexpr std::_Tuple_impl<_Idx, _Head, _Tail ...>::_Tuple_impl(const std::_Tuple_impl<_Idx, _Head, _Tail ...>&) [with long unsigned int _Idx = 3ul, _Head = std::unique_ptr<std::array<unsigned char, 10240ul> >, _Tail = {}, std::_Tuple_impl<_Idx, _Head, _Tail ...> = std::_Tuple_impl<3ul, std::unique_ptr<std::array<unsigned char, 10240ul> > >]’
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/tuple:170:17: error: ‘constexpr std::_Tuple_impl<_Idx, _Head, _Tail ...>::_Tuple_impl(const std::_Tuple_impl<_Idx, _Head, _Tail ...>&) [with long unsigned int _Idx = 3ul, _Head = std::unique_ptr<std::array<unsigned char, 10240ul> >, _Tail = {}, std::_Tuple_impl<_Idx, _Head, _Tail ...> = std::_Tuple_impl<3ul, std::unique_ptr<std::array<unsigned char, 10240ul> > >]’ is implicitly deleted because the default definition would be ill-formed:
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/tuple:170:17: error: use of deleted function ‘std::_Head_base<3ul, std::unique_ptr<std::array<unsigned char, 10240ul> >, false>::_Head_base(const std::_Head_base<3ul, std::unique_ptr<std::array<unsigned char, 10240ul> >, false>&)’
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/tuple:91:12: error: ‘std::_Head_base<3ul, std::unique_ptr<std::array<unsigned char, 10240ul> >, false>::_Head_base(const std::_Head_base<3ul, std::unique_ptr<std::array<unsigned char, 10240ul> >, false>&)’ is implicitly deleted because the default definition would be ill-formed:
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/tuple:91:12: error: use of deleted function ‘std::unique_ptr<_Tp, _Dp>::unique_ptr(const std::unique_ptr<_Tp, _Dp>&) [with _Tp = std::array<unsigned char, 10240ul>, _Dp = std::default_delete<std::array<unsigned char, 10240ul> >, std::unique_ptr<_Tp, _Dp> = std::unique_ptr<std::array<unsigned char, 10240ul> >]’
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/bits/unique_ptr.h:256:7: error: declared here

更新：

我知道上述方法似乎不起作用。但是，不应该以下工作吗？

  std::unique_ptr<buffer_t> buffer = buffers.pop();

  auto t = std::bind(&tcp_client::handle_read_done,
             this,
             std::placeholders::_1,
             std::placeholders::_2,
             std::move(buffer));
  size_t var = 10;
  boost::system::error_code code;
  t(code, var);

handle_read_done的签名在哪里

void tcp_client::handle_read_done(const boost::system::error_code & error, size_t bytes_read, std::unique_ptr<buffer_t> buffer)

感觉好像我遗漏了一些非常明显的东西。

错误信息：

/home/max/dev/rcon/src/net/tcp_client.cpp: In member function ‘void rcon::net::tcp_client::handle_connect_done(const boost::system::error_code&, const string&)’:
/home/max/dev/rcon/src/net/tcp_client.cpp:101:15: error: no match for call to ‘(std::_Bind<std::_Mem_fn<void (rcon::net::tcp_client::*)(const boost::system::error_code&, long unsigned int, std::unique_ptr<std::array<unsigned char, 10240ul> >)>(rcon::net::tcp_client*, std::_Placeholder<1>, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> >)>) (boost::system::error_code&, size_t&)’
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/functional:1130:11: note: candidates are:
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/functional:1201:2: note: template<class ... _Args, class _Result> _Result std::_Bind<_Functor(_Bound_args ...)>::operator()(_Args&& ...) [with _Args = {_Args ...}, _Result = _Result, _Functor = std::_Mem_fn<void (rcon::net::tcp_client::*)(const boost::system::error_code&, long unsigned int, std::unique_ptr<std::array<unsigned char, 10240ul> >)>, _Bound_args = {rcon::net::tcp_client*, std::_Placeholder<1>, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> >}]
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/functional:1215:2: note: template<class ... _Args, class _Result> _Result std::_Bind<_Functor(_Bound_args ...)>::operator()(_Args&& ...) const [with _Args = {_Args ...}, _Result = _Result, _Functor = std::_Mem_fn<void (rcon::net::tcp_client::*)(const boost::system::error_code&, long unsigned int, std::unique_ptr<std::array<unsigned char, 10240ul> >)>, _Bound_args = {rcon::net::tcp_client*, std::_Placeholder<1>, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> >}]
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/functional:1229:2: note: template<class ... _Args, class _Result> _Result std::_Bind<_Functor(_Bound_args ...)>::operator()(_Args&& ...) volatile [with _Args = {_Args ...}, _Result = _Result, _Functor = std::_Mem_fn<void (rcon::net::tcp_client::*)(const boost::system::error_code&, long unsigned int, std::unique_ptr<std::array<unsigned char, 10240ul> >)>, _Bound_args = {rcon::net::tcp_client*, std::_Placeholder<1>, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> >}]
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/functional:1243:2: note: template<class ... _Args, class _Result> _Result std::_Bind<_Functor(_Bound_args ...)>::operator()(_Args&& ...) const volatile [with _Args = {_Args ...}, _Result = _Result, _Functor = std::_Mem_fn<void (rcon::net::tcp_client::*)(const boost::system::error_code&, long unsigned int, std::unique_ptr<std::array<unsigned char, 10240ul> >)>, _Bound_args = {rcon::net::tcp_client*, std::_Placeholder<1>, std::_Placeholder<2>, std::unique_ptr<std::array<unsigned char, 10240ul> >}]

【问题讨论】：

你是如何调用 async_read_some 的？这将需要为您填充缓冲区，它将 boost::asio::buffer 作为第一个参数，然后是回调（参见：boost.org/doc/libs/1_49_0/doc/html/boost_asio/example/echo/… 示例）。通常缓冲区是类成员，不需要作为参数传递给回调，所以不需要绑定它
@mark 我正在从对缓冲区的引用构造一个 boost::asio::buffer。然后我想将 std::unique_ptr 放在回调中，以确保缓冲区继续存在。然后我会将它放回回调中的队列中。
根据下面霍华德的回答，std::bind 创建的仿函数似乎与std::function 或boost::asio 不兼容。因此，您有 2 个选项，要么将 unique_ptr<buffer> 保存在成员变量中，这样它就不需要通过 std::bind 传递，或者从 std::unique_ptr 切换到支持复制语义的 std::shared_ptr（或简单类型） .

标签： c++ c++11 bind unique-ptr

【解决方案1】：

std::bind 适用于仅移动类型。然而，它在这个过程中创建了一个只能移动的函子。 std::function 需要一个可复制构造的函子。听起来boost::asio 也是。

当你调用只移动的bind 函子时，它会将其绑定的参数作为左值传递给目标operator()。因此，如果您的绑定参数之一是只能移动的，则目标 operator() 必须通过（可能是 const）左值引用来获取该参数。

【讨论】：

嗯，为什么 std::function 不能与 move 可构造函子一起使用？
很高兴知道。我仍然想知道 async_read_some 是如何被调用的。
@JohannesSchaub-litb：std::function 类型擦除了它的函子。因此，要实现 std::function 的复制构造函数，必须设置一个虚函数来调用仿函数的复制构造函数。您必须用虚函数指向仿函数的复制构造函数这一事实意味着无论您是否实际实例化 std::function 的复制构造函数，它都会被“使用”。
@Howard 谢谢，这听起来很合理。我可能会改用 shared_ptr 。但是，请参阅我的更新。为什么我什至不能调用函数？
@Howard 啊，我明白了。我想在所有调用虚函数来复制仿函数的情况下，都可以向 std::function 添加一个复制 ctor。虚函数的实现知道 Functor 的类型，并且可以像 return throw_if_noncopyable(_theFunctor); 一样（如果不可复制则抛出，如果可复制则复制）。由于这是一个编译时分支，因此仅当类型可复制时才会使用复制 ctor。这不可行吗？