is_class documented as yielding "true" for unions, but documentation contradicts that

[schaub.johannes@…]

The is_class documentation at http://www.boost.org/doc/libs/1_46_1/libs/type_traits/doc/html/boost_typetraits/reference/is_class.html says

"Inherits: If T is a (possibly cv-qualified) class type then inherits from true_type, otherwise inherits from false_type"

This means that is_class shall be derived from true_type if T is an union, because an union is a class type. But the "Compiler Compatibility" section contains some really confusing text:

"Without (some as yet unspecified) help from the compiler, we cannot distinguish between union and class types, as a result this type will erroneously inherit from true_type for union types."

[Thomas Heller]

Even the cited standard paragraph states this:

3.9.2: "unions, which are classes capable of containing objects of different types at different times, 9.5;"

[schaub.johannes@…]

Also at 9p4: "A union is a class defined with the class-key union; its members are public by default and it holds only one data member at a time (9.5)." and the remaining text of the spec.

[Michel MORIN <mimomorin@…>]

A patch for is_class.qbk.

[Michel MORIN <mimomorin@…>]

C++0x FDIS explicitly excludes a union type for is_class. I attached a patch to sync with this.

[Michel MORIN <mimomorin@…>]

A patch for is_empty.qbk.

[Michel MORIN <mimomorin@…>]

A patch for fixing comments in intrinsics.hpp.

[Michel MORIN <mimomorin@…>]

Similarly, is_empty.qbk needs to be fixed (a patch attached). I also fixed comments in intrinsics.hpp accordingly.

[John Maddock]

(In [73942]) Documentation tweaks. Fixes #5666.