Question

以下代码在我尝试的每个编译器上编译都很好（gcc 4.9.2，clang 3.6和VS 2015）。但是，VS 2013更新4解决了错误，我将在下面详述。这是编译器中的错误吗？

#include <iostream>
#include <functional>

template<typename Func>
struct Bar
{
    Func f_;
    Bar(Func f) : f_(f) { }
    void operator()() const
    {
        f_();
    }
};

template<typename T>
void Baz(T const& t)
{
    Bar<T> b(t);
    b();
}

struct Foo 
{ 
    Foo()
    {
        auto r = std::bind(&Foo::DoFoo, this);
        Baz(r);
    }
    void DoFoo() { std::cout << "Doing Foo!\n"; } 
};

int main()
{
    Foo f;
    return 0;
}

错误列表如下：

1>doodle.cpp(15): error C3848: expression having type 'const std::_Bind<true,void,std::_Pmf_wrap<void (__thiscall Foo::* )(void),void,Foo,>,Foo *const >' would lose some const-volatile qualifiers in order to call 'void std::_Bind<true,void,std::_Pmf_wrap<void (__thiscall Foo::* )(void),void,Foo,>,Foo *const >::operator ()<>(void)'
1>          doodle.cpp(14) : while compiling class template member function 'void Bar<T>::operator ()(void) const'
1>          with
1>          [
1>              T=std::_Bind<true,void,std::_Pmf_wrap<void (__thiscall Foo::* )(void),void,Foo,>,Foo *const >
1>          ]
1>          doodle.cpp(23) : see reference to function template    instantiation 'void Bar<T>::operator ()(void) const' being compiled
1>          with
1>          [
1>              T=std::_Bind<true,void,std::_Pmf_wrap<void (__thiscall Foo::* )(void),void,Foo,>,Foo *const >
1>          ]
1>          doodle.cpp(22) : see reference to class template instantiation 'Bar<T>' being compiled
1>          with
1>          [
1>              T=std::_Bind<true,void,std::_Pmf_wrap<void (__thiscall Foo::* )(void),void,Foo,>,Foo *const >
1>          ]
1>          doodle.cpp(31) : see reference to function template instantiation 'void Baz<std::_Bind<true,void,std::_Pmf_wrap<void (__thiscall Foo::* )(void),void,Foo,>,Foo *const >>(const T &)' being compiled
1>          with
1>          [
1>              T=std::_Bind<true,void,std::_Pmf_wrap<void (__thiscall Foo::* )(void),void,Foo,>,Foo *const >
1>          ]

我认为它希望DoFoo（）成为const成员函数，但修复它并没有帮助。

Answer 1

这似乎是一个VS2013编译器错误，有两种方法可以解决它：

使用std :: function而不是auto来存储对成员函数的调用

std::function<void()> r = std::bind(&Foo::DoFoo, this);

或者从Bar

中的函数调用operator（）中删除const

template<typename Func>
struct Bar
{
    Func f_;
    Bar(Func f) : f_(f) { }
    void operator()() // const
    {
        f_();
    }
};

const调用操作符调用绑定的非const成员函数

1 个答案: