On Tue, 8 May 2012, John Maddock wrote:
Folks I'm having some difficulties understanding the subtleties of enable_if, consider:
using namespace boost;
template <unsigned B> struct dummy {};
template <unsigned B, class Integer> typename boost::enable_if<mpl::and_<is_signed<Integer>, mpl::bool_<(sizeof(Integer) <= sizeof(long))> > >::type bar(dummy<B>&, const Integer&) { } template <unsigned B, class Integer> typename boost::enable_if<mpl::and_<is_unsigned<Integer>, mpl::bool_<(sizeof(Integer) <= sizeof(long))> > >::type bar(dummy<B>&, const Integer&) { }
Then calling:
dummy<2> d; bar(d, 2);
Leads to an ambiguity between the two overloads (both gcc and VC++10), how can that be?
The code works for me (as written above) on GCC 4.7 (both with -m32 and -m64 on x86-64, and with -std=c++98 and -std=c++0x, -ansi -pedantic). I don't see a reason that it would be ambiguous. -- Jeremiah Willcock