error: no member named 'rank_' in 'EndIndex' - c++

Question

I am trying to use the automatic differentiation library Adept and I made it work with gcc 4.9.0 and icc 16.0.2 but failed with VS 2017 and Clang 4.0.1
I have reduced the problem to the following snippet and, while I am addressing the issue with the library creators, for the sake of the knowledge I would like to know why this piece of code works in the two mentioned compilers and fails to build in the other two.
template <typename A>
struct Expression
{
static const int rank = A::rank_;
};
struct EndIndex : public Expression<EndIndex>
{
static const int rank_ = 0;
};
int main(int argc, char ** argv)
{
return 0;
}
Output for VS 2017 is:
1>------ Build started: Project: Test, Configuration: Debug Win32 ------
1>Source.cpp
1>d:\Test\source.cpp(4): error C2039: 'rank_': is not a member of 'EndIndex'
1>d:\Test\source.cpp(7): note: see declaration of 'EndIndex'
1>d:\Test\source.cpp(8): note: see reference to class template instantiation 'Expression<EndIndex>' being compiled
1>d:\Test\source.cpp(4): error C2065: 'rank_': undeclared identifier
1>d:\Test\source.cpp(4): error C2131: expression did not evaluate to a constant
1>d:\Test\source.cpp(4): note: failure was caused by non-constant arguments or reference to a non-constant symbol
1>d:\Test\source.cpp(4): note: see usage of 'rank_'
1>Done building project "Test.vcxproj" -- FAILED.
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
And output for Clang 4.0.1:
source.cpp:4:37: error: no member named 'rank_' in 'EndIndex'
static const int rank = A::rank_;
~~~^
source.cpp:7:38: note: in instantiation of template class 'Expression<EndIndex>' requested here
struct EndIndex : public Expression<EndIndex>

Answer 1

It probably happens because rank_ is not defined at that stage.
The following fixes it for Apple LLVM version 9.0.0 (clang-900.0.38):
template <typename A>
struct Expression
{
static const int rank;
};
struct EndIndex : public Expression<EndIndex>
{
static const int rank_ = 0;
};
template <typename A>
const int Expression<A>::rank = A::rank_;

Answer 2

Visual C++ and clang are simply unable to find rank_ member of EndIndex because it's being accessed before declared. Such fancy code often leads to problems in some environments.