我正在尝试使用 boost::asio 并遇到了一些问题。
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));
如果我排除 std::move(buffer)，一切正常，当然是从 handle_read_done 的签名和作为 std::bind 中传递的参数。
当试图将它传递给 boost::asio::async_read_some 时，它提示从 std::bind 返回的对象上隐式删除了函数，我认为元组上的删除函数是因为可移动性，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 std::function 中，它应该与 boost 调用的签名相匹配，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，但当然我不能对其调用任何东西。
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:
据我了解，上述内容似乎行不通。但是，下面的方法不应该起作用吗？
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);
凡签名handle_read_done是
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> >}]
最佳答案
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仿函数。 std::function 需要一个可复制构造的仿函数。听起来 boost::asio 也是如此。
当您调用仅移动的 bind 仿函数时，它会将其绑定(bind)参数作为左值传递给目标 operator()。因此，如果您的绑定(bind)参数之一是仅移动的，则目标 operator() 必须通过(可能是 const)左值引用来获取该参数。
关于c++ - std::bind 通常与仅移动类型一起使用，特别是 std::unique_ptr 吗？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/9955714/
我在我的项目目录中完成了compasscreate.和compassinitrails。几个问题:我已将我的.sass文件放在public/stylesheets中。这是放置它们的正确位置吗？当我运行compasswatch时，它不会自动编译这些.sass文件。我必须手动指定文件:compasswatchpublic/stylesheets/myfile.sass等。如何让它自动运行？文件ie.css、print.css和screen.css已放在stylesheets/compiled。如何在编译后不让它们重新出现的情况下删除它们？我自己编译的.sass文件编译成compiled/t
我的瘦服务器配置了nginx，我的ROR应用程序正在它们上运行。在我发布代码更新时运行thinrestart会给我的应用程序带来一些停机时间。我试图弄清楚如何优雅地重启正在运行的Thin实例，但找不到好的解决方案。有没有人能做到这一点？ 最佳答案 #Restartjustthethinserverdescribedbythatconfigsudothin-C/etc/thin/mysite.ymlrestartNginx将继续运行并代理请求。如果您将Nginx设置为使用多个上游服务器，例如server{listen80;server
它不等于主线程的binding，这个toplevel作用域是什么？此作用域与主线程中的binding有何不同？>ruby-e'putsTOPLEVEL_BINDING===binding'false 最佳答案 事实是，TOPLEVEL_BINDING始终引用Binding的预定义全局实例，而Kernel#binding创建的新实例>Binding每次封装当前执行上下文。在顶层，它们都包含相同的绑定(bind)，但它们不是同一个对象，您无法使用==或===测试它们的绑定(bind)相等性。putsTOPLEVEL_BINDINGput
如果我使用ruby版本2.5.1和Rails版本2.3.18会怎样？我有基于rails2.3.18和ruby1.9.2p320构建的rails应用程序，我只想升级ruby的版本，而不是rails，这可能吗？我必须面对哪些挑战？ 最佳答案 GitHub维护apublicfork它有针对旧Rails版本的分支，有各种变化，它们一直在运行。有一段时间，他们在较新的Ruby版本上运行较旧的Rails版本，而不是最初支持的版本，因此您可能会发现一些关于需要向后移植的有用提示。不过，他们现在已经有几年没有使用2.3了，所以充其量只能让更
如何将send与+=一起使用？a=20;a.send"+=",10undefinedmethod`+='for20:Fixnuma=20;a+=10=>30 最佳答案 恐怕你不能。+=不是方法，而是语法糖。参见http://www.ruby-doc.org/docs/ProgrammingRuby/html/tut_expressions.html它说Incommonwithmanyotherlanguages,Rubyhasasyntacticshortcut:a=a+2maybewrittenasa+=2.你能做的最好的事情是:
我正在尝试在Rails上安装ruby，到目前为止一切都已安装，但是当我尝试使用rakedb:create创建数据库时，我收到一个奇怪的错误:dyld:lazysymbolbindingfailed:Symbolnotfound:_mysql_get_client_infoReferencedfrom:/Library/Ruby/Gems/1.8/gems/mysql2-0.3.11/lib/mysql2/mysql2.bundleExpectedin:flatnamespacedyld:Symbolnotfound:_mysql_get_client_infoReferencedf
我对如何计算通过{%assignvar=0%}赋值的变量加一完全感到困惑。这应该是最简单的任务。到目前为止，这是我尝试过的:{%assignamount=0%}{%forvariantinproduct.variants%}{%assignamount=amount+1%}{%endfor%}Amount:{{amount}}结果总是0。也许我忽略了一些明显的东西。也许有更好的方法。我想要存档的只是获取运行的迭代次数。 最佳答案 因为{{incrementamount}}将输出您的变量值并且不会影响{%assign%}定义的变量，我
我已经找到了几个使用datamapper的示例，并且能够让它们正常工作。不过，所有这些示例都是针对sqlite数据库的。我正在尝试将数据映射器与postgresql一起使用。我将datamapper中的调用从sqlite3更改为postgres，并且我已经安装了dm-postgres-adapter。但它仍然不起作用。我还需要做什么？ 最佳答案 与SQLite不同，PostgreSQL不将数据库存储在单个文件中。在你拥有createdyourdatabase之后，尝试这样的事情:DataMapper.setup:default,{:
我有一个数组数组，想将元素附加到子数组。+=做我想做的，但我想了解为什么push不做。我期望的行为(并与+=一起工作):b=Array.new(3,[])b[0]+=["apple"]b[1]+=["orange"]b[2]+=["frog"]b=>[["苹果"],["橙子"],["Frog"]]通过推送，我将推送的元素附加到每个子数组(为什么？):a=Array.new(3,[])a[0].push("apple")a[1].push("orange")a[2].push("frog")a=>[[“苹果”、“橙子”、“Frog”]、[“苹果”、“橙子”、“Frog”]、[“苹果”、“
我经常将预配置的lambda插入可枚举的方法中，例如“map”、“select”等。但是“注入(inject)”的行为似乎有所不同。例如与mult4=lambda{|item|item*4}然后(5..10).map&mult4给我[20,24,28,32,36,40]但是，如果我制作一个2参数lambda用于像这样的注入(inject)，multL=lambda{|product,n|product*n}我想说(5..10).inject(2)&multL因为“inject”有一个可选的单个初始值参数，但这给了我......irb(main):027:0>(5..10).inject