[英]Error in VS2013 when attempting to partially specialize a class template with another class template
给定以下类和函数模板:
template <typename WrappedType, ParameterType ParamType, bool IsOutputParameter>
class WrappedParameter; // Definition left out for brevity
template <typename T>
struct ParameterUnwrapper
{
static T UnwrapParameter(const T& in_param)
{
return in_param;
}
};
template <typename T, ParameterType ParamType, bool IsOutputParameter>
struct ParameterUnwrapper<WrappedParameter<T, ParamType, IsOutputParameter>>
{
static T UnwrapParameter(const WrappedParameter<T, ParamType, IsOutputParameter>& in_param)
{
return in_param.GetWrapped();
}
};
template <typename T>
T UnwrapParameter(T in_param)
{
return Impl::ParameterUnwrapper<T>::UnwrapParameter(in_param);
}
template <typename T>
Impl::WrappedParameter<T, Impl::POINTER_PARAMETER, true> WrapOutputPointerParameter(T in_param)
{
return Impl::WrappedParameter<T, Impl::POINTER_PARAMETER, true>(in_param);
}
template <typename MemFunc, typename ...Args>
HRESULT ExecuteAndLog(
MemFunc in_memberFunction,
const std::string& in_methodName,
Args... args) //-> decltype((m_wrapped->*in_memberFunction)(UnwrapParameter(args)...))
{
return ExecuteFunctorAndLog(
[&]() { return (m_wrapped->*in_memberFunction)(UnwrapParameter(args)...); },
in_methodName,
args...);
}
以下调用:(ExecuteAndLog)
HRESULT STDMETHODCALLTYPE AccessorWrapper::AddRefAccessor(
HACCESSOR hAccessor,
DBREFCOUNT *pcRefCount)
{
return ExecuteAndLog(
&IAccessor::AddRefAccessor,
"AddRefAccessor",
hAccessor,
WrapOutputPointerParameter(pcRefCount));
}
给我错误:
error C2664: 'HRESULT (HACCESSOR,DBREFCOUNT *)' : cannot convert argument 2 from 'Impl::WrappedParameter<DBREFCOUNT *,POINTER_PARAMETER,true>' to 'DBREFCOUNT *'
No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
see reference to function template instantiation 'ExecuteAndLog<HRESULT(__stdcall IAccessor::* )(HACCESSOR,DBREFCOUNT *),HACCESSOR, Impl::WrappedParameter<DBREFCOUNT *,POINTER_PARAMETER,true>>(MemFunc,const std::string &,HACCESSOR,Impl::WrappedParameter<DBREFCOUNT *,POINTER_PARAMETER,true>)' being compiled
with
[
MemFunc=HRESULT (__stdcall IAccessor::* )(HACCESSOR,DBREFCOUNT *)
]
see reference to function template instantiation 'ExecuteAndLog<HRESULT(__stdcall IAccessor::* )(HACCESSOR,DBREFCOUNT *),HACCESSOR,Impl::WrappedParameter<DBREFCOUNT *,POINTER_PARAMETER,true>>(MemFunc,const std::string &,HACCESSOR,Impl::WrappedParameter<DBREFCOUNT *,POINTER_PARAMETER,true>)' being compiled
with
[
MemFunc=HRESULT (__stdcall IAccessor::* )(HACCESSOR,DBREFCOUNT *)
]
我想我搞砸了ParameterUnwrapper的部分专业化(或者我的方法是错误的)。 有什么建议吗?
更多信息:
Impl是一个嵌套的名称空间(除ExecuteAndLog外,所有提供的模板均位于该名称空间中)
在这种情况下,m_wrapped的类型为IAccessor *(COM接口)。
enum ParameterType
{
POINTER_PARAMETER,
ARRAY_PARAMETER
};
更新:这是一个自包含的示例: http : //codepad.org/lwTzVImb
我在VS2013中遇到的错误是:
error C2664: 'int (int,int **,size_t *)' : cannot convert argument 2 from 'WrappedParameter<int **,ARRAY_PARAMETER,true>' to 'int **'
No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
see reference to function template instantiation 'int ExecuteAndLog<int(__thiscall A::* )(int,int **,size_t *),int,WrappedParameter<int **,ARRAY_PARAMETER,true>,size_t*>(MemFunc,const std::string &,int,WrappedParameter<int **,ARRAY_PARAMETER,true>,size_t *)' being compiled
with
[
MemFunc=int (__thiscall A::* )(int,int **,size_t *)
]
我想到了!
问题是UnwrapParameter的返回类型。 一旦我将其声明更改为
template <typename T>
auto UnwrapParameter(T in_param) -> decltype(Impl::ParameterUnwrapper<T>::UnwrapParameter(in_param))
它编译了。 令人遗憾的是,编译器没有抱怨该函数的定义,而不是信任其声明的返回值。
我现在还有其他一些问题,但至少我已经取得了进展。
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