我无法检测到为什么这不能编译。我有一些返回 a 的 lambda 函数std::function
基于一些论点。
我已将问题范围缩小到此代码片段(它不使用 lambda,但完美地重现了我的错误):
#include <functional>
#include <iostream>
struct foo {
template<class T>
void bar(T data) {
std::cout << data << "\n";
}
};
void some_fun(const std::function<void(int)> &f) {
f(12);
}
int main() {
foo x;
auto f = std::bind(&foo::bar<int>, x, std::placeholders::_1);
auto w = std::bind(some_fun, f);
w();
}
致电给w()
产生那些可爱的 gcc 错误输出之一,我无法弄清楚出了什么问题。这是 gcc 4.6.1 回显的错误:
g++ -std=c++0x test.cpp -o test
test.cpp: In function ‘int main()’:
test.cpp:20:7: error: no match for call to ‘(std::_Bind<void (*(std::_Bind<std::_Mem_fn<void (foo::*)(int)>(foo, std::_Placeholder<1>)>))(const std::function<void(int)>&)>) ()’
/usr/include/c++/4.6/functional:1130:11: note: candidates are:
/usr/include/c++/4.6/functional:1201:2: note: template<class ... _Args, class _Result> _Result std::_Bind<_Functor(_Bound_args ...)>::operator()(_Args&& ...) [with _Args = {_Args ...}, _Result = _Result, _Functor = void (*)(const std::function<void(int)>&), _Bound_args = {std::_Bind<std::_Mem_fn<void (foo::*)(int)>(foo, std::_Placeholder<1>)>}]
/usr/include/c++/4.6/functional:1215:2: note: template<class ... _Args, class _Result> _Result std::_Bind<_Functor(_Bound_args ...)>::operator()(_Args&& ...) const [with _Args = {_Args ...}, _Result = _Result, _Functor = void (*)(const std::function<void(int)>&), _Bound_args = {std::_Bind<std::_Mem_fn<void (foo::*)(int)>(foo, std::_Placeholder<1>)>}]
/usr/include/c++/4.6/functional:1229:2: note: template<class ... _Args, class _Result> _Result std::_Bind<_Functor(_Bound_args ...)>::operator()(_Args&& ...) volatile [with _Args = {_Args ...}, _Result = _Result, _Functor = void (*)(const std::function<void(int)>&), _Bound_args = {std::_Bind<std::_Mem_fn<void (foo::*)(int)>(foo, std::_Placeholder<1>)>}]
/usr/include/c++/4.6/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 = void (*)(const std::function<void(int)>&), _Bound_args = {std::_Bind<std::_Mem_fn<void (foo::*)(int)>(foo, std::_Placeholder<1>)>}]
Here, f
应该是一些可调用对象,它以 int 作为参数并调用x.bar(int)
使用它。另一方面,w
只是一个可调用对象,它调用some_fun(f)
, being f
上面提到的可调用对象,它具有预期的签名some_fun
的参数。
我错过了什么吗?我可能不知道如何实际混合std::bind
and std::function
.