Proposed resolution:

Resolved by paper n3142.

[ 2010-10-24 Daniel adds: ]

Accepting n3142 would solve this issue.

[ Resolution proposed by ballot comment ]

Specify that std::is_constructible and std::is_convertible will return true only for public constructors/conversion functions.

Addresses DE-18

Several type traits require compiler support, e.g. std::is_constructible or std::is_convertible. Their current specification seems to imply, that the corresponding test expressions should be well-formed, even in absense of access:

class X { X(int){} };
constexpr bool test = std::is_constructible<X, int>::value;

The specification does not clarify the context of this test and because it already goes beyond normal language rules, it's hard to argue by means of normal language rules what the context and outcome of the test should be.