[boost] typeof: lvalue preserving

From: Vertleyb (vertleyb_at_[hidden])
Date: 2004-07-22 00:02:23

One more addition to the typeof library is a macro, that, unlike
BOOST_TYPEOF(), which removes top-level consts and references, attempts to
be closer to the decltype, by preserving lvalue-ness of its argument:

BOOST_TYPEOF_PRESERVE_LVALUE(expr)

I do admit that the name is quite clumzy :(

It is directly based on the rules of binding a reference.  The following
table outlines which types are returned:

Expression              lvalue?     typeof_preserve_lvalue(expression)
----------              -------     ------
int n;                       lvalue      int&
const int m;             lvalue      const int&
int& rn = n;             lvalue      int&
const int& rm;         lvalue      const int&
int foo1();                              int
const int foo2();                     const int& (unfortunately, in both
VC7.1 and GCC 3.3)
int& foo3();            lvalue      int&
const int& foo4();   lvalue      const int&
int(21)                                   int
21                                         int

The BOOST_AUTO remains based on the BOOST_TYPEOF.  The references, in the
same way as proposed in
http://www.osl.iu.edu/~jajarvi/publications/papers/decltype_n1478.pdf,
should be specified explicitly:

int& foo();

BOOST_AUTO(v, foo()); // auto v = foo();
BOOST_AUTO(&r, foo()); // auto& r = foo();
BOOST_AUTO(const& cr, foo()); // auto const& cr = foo();

See http://groups.yahoo.com/group/boost/files/typeof.zip (or Spirit
repository, TYPEOF_DEV branch).

As always any comments are welcome.

Thanks,
Arkadiy