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.
template <typename A, typename B = typename A::C::D>开发者_运维技巧; // 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:
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. If I replace template <typename> class E
with just typename E
and make that foo<E>
, it works fine. If explicitly specify the second template argument to foo
in line 8, like so, it works fine:
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;
to the definition of foo
, that also works fine.
Any ideas? What bit of C++ rules am I missing?
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:
https://connect.microsoft.com/VisualStudio/feedback/details/576196
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