[英]Using member of template class to instantiate template default parameter in MSVC++
The following piece of code is a reduced sample from the large project I'm trying to port from GCC/G++ to Microsoft Visual C++ 2010. It compiles fine with G++, but with MSVC++, it throws errors, and I'm having trouble understanding why. 下面的代码是我试图从GCC / G ++移植到Microsoft Visual C ++ 2010的大型项目的简化示例。它可以在G ++上很好地编译,但是在MSVC ++上,它会引发错误,并且我很难理解为什么。
template <typename A, typename B = typename A::C::D> // line 1
struct foo
{
typedef int type;
};
template <template <typename> class E, typename T>
typename foo<E<T> >::type // line 8
bar(){}
The error messages from MSVC++ are: 来自MSVC ++的错误消息是:
example1.cpp(1) : error C2027: use of undefined type 'E<T>'
example1.cpp(8) : error C2146: syntax error : missing ',' before identifier 'D'
example1.cpp(8) : error C2065: 'D' : undeclared identifier
I've tried a few changes to narrow down the problem a bit, and while I don't fully understand it, here's what I've discovered: If in line 1 I replace A::C::D
with A::C
, it works fine. 我尝试了一些更改来缩小问题的范围,虽然我不太了解,但是发现的是:如果在第1行中,我将
A::C::D
替换为A::C
,效果很好。 If I replace template <typename> class E
with just typename E
and make that foo<E>
, it works fine. 如果我更换
template <typename> class E
只用typename E
并作出foo<E>
它工作正常。 If explicitly specify the second template argument to foo
in line 8, like so, it works fine: 如果像这样在第8行中显式指定
foo
的第二个模板参数,则效果很好:
typename foo<E<T>, typename E<T>::C::D>::type // line 8
And, if I replace the use of A::C::D
with something innocuous like typename B = A
in line 1, but add a different use of A::C::D
as typedef typename A::C::D qux;
而且,如果我在第1行中将
A::C::D
替换为无害的名称,例如typename B = A
,但添加另一种使用A::C::D
作为typedef typename A::C::D qux;
to the definition of foo
, that also works fine. 按照
foo
的定义,也可以正常工作。
Any ideas? 有任何想法吗? What bit of C++ rules am I missing?
我缺少什么C ++规则?
I reported this as a bug with Microsoft as per jpalecek's suggestion, and Microsoft has confirmed that it is indeed a fault in their compiler: 根据jpalecek的建议,我将其报告为Microsoft的错误,并且Microsoft已确认这确实是其编译器中的错误:
https://connect.microsoft.com/VisualStudio/feedback/details/576196 https://connect.microsoft.com/VisualStudio/feedback/details/576196
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