C++ 为什么可以'；对实例化的类模板A的引用（从（非模板）类B继承）是否转换为对B的引用？

我有一个这样的类层次结构（这是实际的类，但我清理了它）：

但我在编译时得到：

In file included from /opt/local/include/gcc47/c++/bits/move.h:57:0,
                 from /opt/local/include/gcc47/c++/bits/stl_pair.h:61,
                 from /opt/local/include/gcc47/c++/bits/stl_algobase.h:65,
                 from /opt/local/include/gcc47/c++/bits/char_traits.h:41,
                 from /opt/local/include/gcc47/c++/ios:41,
                 from /opt/local/include/gcc47/c++/ostream:40,
                 from /opt/local/include/gcc47/c++/iostream:40,
                 from json2cli/main.cpp:9:
/opt/local/include/gcc47/c++/type_traits: In instantiation of 'struct std::_Result_of_impl<false, false, std::_Mem_fn<void (Experiment::*)(Notifiable&)>, MyExperiment, Batch<MyExperiment> >':
/opt/local/include/gcc47/c++/type_traits:1857:12:   required from 'class std::result_of<std::_Mem_fn<void (Experiment::*)(Notifiable&)>(MyExperiment, Batch<MyExperiment>)>'
/opt/local/include/gcc47/c++/functional:1563:61:   required from 'struct std::_Bind_simple<std::_Mem_fn<void (Experiment::*)(Notifiable&)>(MyExperiment, Batch<MyExperiment>)>'
/opt/local/include/gcc47/c++/thread:133:9:   required from 'std::thread::thread(_Callable&&, _Args&& ...) [with _Callable = void (Experiment::*)(Notifiable&); _Args = {MyExperiment&, Batch<MyExperiment>&}]'
json2cli/batch.hh:86:46:   required from 'void Batch<Exp>::run() [with Exp = MyExperiment]'
json2cli/main.cpp:113:15:   required from here
/opt/local/include/gcc47/c++/type_traits:1834:9: error: no match for call to '(std::_Mem_fn<void (Experiment::*)(Notifiable&)>) (MyExperiment, Batch<MyExperiment>)'
In file included from /opt/local/include/gcc47/c++/memory:81:0,
                 from json2cli/parameterexpression.hh:19,
                 from json2cli/main.cpp:13:
/opt/local/include/gcc47/c++/functional:525:11: note: candidates are:
/opt/local/include/gcc47/c++/functional:548:7: note: _Res std::_Mem_fn<_Res (_Class::*)(_ArgTypes ...)>::operator()(_Class&, _ArgTypes ...) const [with _Res = void; _Class = Experiment; _ArgTypes = {Notifiable&}]
/opt/local/include/gcc47/c++/functional:548:7: note:   no known conversion for argument 1 from 'MyExperiment' to 'Experiment&'
/opt/local/include/gcc47/c++/functional:553:7: note: _Res std::_Mem_fn<_Res (_Class::*)(_ArgTypes ...)>::operator()(_Class*, _ArgTypes ...) const [with _Res = void; _Class = Experiment; _ArgTypes = {Notifiable&}]
/opt/local/include/gcc47/c++/functional:553:7: note:   no known conversion for argument 1 from 'MyExperiment' to 'Experiment*'
/opt/local/include/gcc47/c++/functional:559:2: note: template<class _Tp> _Res std::_Mem_fn<_Res (_Class::*)(_ArgTypes ...)>::operator()(_Tp&, _ArgTypes ...) const [with _Tp = _Tp; _Res = void; _Class = Experiment; _ArgTypes = {Notifiable&}]
/opt/local/include/gcc47/c++/functional:559:2: note:   template argument deduction/substitution failed:
In file included from /opt/local/include/gcc47/c++/bits/move.h:57:0,
                 from /opt/local/include/gcc47/c++/bits/stl_pair.h:61,
                 from /opt/local/include/gcc47/c++/bits/stl_algobase.h:65,
                 from /opt/local/include/gcc47/c++/bits/char_traits.h:41,
                 from /opt/local/include/gcc47/c++/ios:41,
                 from /opt/local/include/gcc47/c++/ostream:40,
                 from /opt/local/include/gcc47/c++/iostream:40,
                 from json2cli/main.cpp:9:
/opt/local/include/gcc47/c++/type_traits:1834:9: note:   cannot convert 'std::declval<Batch<MyExperiment> >()' (type 'Batch<MyExperiment>') to type 'Notifiable&'

在/opt/local/include/gcc47/c++/bits/move.h:57:0中包含的文件中，
从/opt/local/include/gcc47/c++/bits/stl_pair.h:61，
从/opt/local/include/gcc47/c++/bits/stl_algobase.h:65，
from/opt/local/include/gcc47/c++/bits/char_traits.h:41，
从/opt/local/include/gcc47/c++/ios:41，
从/opt/local/include/gcc47/c++/ostream:40，
从/opt/local/include/gcc47/c++/iostream:40，
来自json2cli/main.cpp:9：
/opt/local/include/gcc47/c++/type_traits:在“struct std:：_Result_of_impl”的实例化中：
/opt/local/include/gcc47/c++/type_traits:1857:12:class std:：result_of'
/opt/local/include/gcc47/c++/functional:1563:61:从“struct std:：_Bind_simple”中需要
/opt/local/include/gcc47/c++/thread:133:9:std:：thread（_Callable&&，_Args&&&…[带_Callable=void（实验：：*）（Notifiable&）；_Args={MyExperiment&，Batch&}中的必填项
json2cli/batch.hh:86:46:来自“void batch:：run（）[with Exp=MyExperiment]”的必填项
json2cli/main.cpp:113:15:此处需要
/opt/local/include/gcc47/c++/type_traits:1834:9:错误：调用“（std:：_Mem_fn）（MyExperiment，Batch）”不匹配
在/opt/local/include/gcc47/c++/memory:81:0中包含的文件中，
从json2cli/parameterexpression.hh:19，
来自json2cli/main.cpp:13：
/opt/local/include/gcc47/c++/functional:525:11：注：候选人包括：
/opt/local/include/gcc47/c++/functional:548:7:注意：_resstd:：_Mem_fn:：operator（）（_Class&，_ArgTypes…）const[with _Res=void；_Class=Experiment；_ArgTypes={应呈报&]
/opt/local/include/gcc47/c++/functional:548:7:注意：参数1从'MyExperiment'到'Experiment&'没有已知的转换
/opt/local/include/gcc47/c++/functional:553:7:注意：_resstd:：_Mem_fn:：operator（）（_Class*，_ArgTypes…）const[with _Res=void；_Class=Experiment；_ArgTypes={应呈报&}]
/opt/local/include/gcc47/c++/functional:553:7:注意：参数1从“MyExperiment”到“Experiment*”没有已知的转换
/opt/local/include/gcc47/c++/functional:559:2:注意：模板_resstd:：_Mem_fn:：operator（）（_Tp&，_ArgTypes…）const[带_Tp=_Tp；_Res=void；_Class=Experiment；_ArgTypes={应呈报&}]
/opt/local/include/gcc47/c++/functional:559:2:注意：模板参数推断/替换失败：
在/opt/local/include/gcc47/c++/bits/move.h:57:0中包含的文件中，
从/opt/local/include/gcc47/c++/bits/stl_pair.h:61，
从/opt/local/include/gcc47/c++/bits/stl_algobase.h:65，
from/opt/local/include/gcc47/c++/bits/char_traits.h:41，
从/opt/local/include/gcc47/c++/ios:41，
从/opt/local/include/gcc47/c++/ostream:40，
从/opt/local/include/gcc47/c++/iostream:40，
来自json2cli/main.cpp:9：
/opt/local/include/gcc47/c++/type_traits:1834:9:注意：无法将'std:：declval（）'（类型'Batch'）转换为'Notifiable&'type

看起来我不能期望将任何

批处理

概括为函数调用的

应报告

。你能证实吗

更新对不起，我以为我可以避免在问题中转储所有代码，但事实上，我为

Batch:：run（）

生成线程的方式肯定有问题。仍然缺少一些细节，但我认为它们并不相关（例如，我如何为实验生成参数）

---

谢谢

您的错误不在您向我们展示的代码中，您在代码中尝试绑定您的

运行

，并使用

std:：thread

创建线程，这就是问题所在，因为它无法为绑定函数创建正确的结构，最简单的解决方法是编写您自己的包装器：

template< class Expr >
struct my_bind {
    my_bind( Expr& e, Notifiable& n ) : e_( e ), n_(n) {}
    void operator()() {e_.run(n_);}
    Expr& e_;
    Notifiable& n_;
};

模板
构造我的绑定{
我的约束（Expr&e，Notifiable&n）：e（e），n（n）{}
void操作符（）
出口和出口；
应呈报的&n；
};

---

然后使用您自己的包装器启动函数，我不能肯定，但我认为这是编译器中的一个错误（所有编译器都有这个错误：GCC，MSVC，…），当表达式变得复杂时，它们无法在

std:：bind

中使用它

您的错误不在您向我们展示的代码中，您试图在代码中绑定您的

运行

，并使用

std:：thread

创建线程，这就是问题所在，因为它无法为绑定函数创建正确的结构，最简单的解决方法是编写您自己的包装器：

template< class Expr >
struct my_bind {
    my_bind( Expr& e, Notifiable& n ) : e_( e ), n_(n) {}
    void operator()() {e_.run(n_);}
    Expr& e_;
    Notifiable& n_;
};

模板
构造我的绑定{
我的约束（Expr&e，Notifiable&n）：e（e），n（n）{}
void操作符（）
出口和出口；
应呈报的&n；
};

然后使用您自己的包装器启动函数，我不能肯定，但我认为这是编译器中的一个错误（所有编译器都有这个错误：GCC，MSVC，…），当表达式变得复杂时，它们无法在

std:：bind

中使用它

变化

 std::thread t(&Exp::run, e, *this);

到

或者，如果您真的希望线程从

*继承副本，请执行以下操作：

std::thread t([](Exp&& e, Batch&& b) { e.run(b); }, std::move(e), *this);

错误的根源（至少是消息引用的一个）是特定的
std:：thread
构造函数的语义（这里我不想公开，这有点血腥）。如果您已经熟悉语义
std:：bind
（它们确实有自己的怪癖），那么您可以遵循它：

std::thread t(std::bind(&Exp::run, std::move(e), std::ref(*this));

（同样，根据您的需要，
std:：ref（*this）
可以替换为
*this
。
更改

 std::thread t(&Exp::run, e, *this);

到

或者如果您真的打算让线程从
*继承一个副本，那么
std::thread t(std::bind(&Exp::run, std::move(e), std::ref(*this));