[Boost-users] [proto] char vs. int behaviour when matching

Subject: [Boost-users] [proto] char vs. int behaviour when matching
From: Maurizio Vitale (maurizio.vitale_at_[hidden])
Date: 2009-09-02 16:28:10

Proto behaves in a different way when matching terminal<char> and
terminal<int>.
The only difference I'm aware is that it is implementation defined
whether 'char' means 'signed char' or 'unsigned char' but it has to mean
one of the two. I was surprised to hit the following:

struct char_grammar : proto::or_<
  proto::terminal<signed char>,
  proto::terminal<unsigned char>
  >
{};

struct extended_char_grammar : proto::or_<
  proto::terminal<char>,
  proto::terminal<signed char>,
  proto::terminal<unsigned char>
  >
{};

struct int_grammar : proto::or_<
  proto::terminal<signed int>,
  proto::terminal<unsigned int>
  >
{};

int main()
{
  // WHY _NOT?
  BOOST_MPL_ASSERT_NOT ((proto::matches<proto::terminal<char>, char_grammar>));
  BOOST_MPL_ASSERT ((proto::matches<proto::terminal<char>, extended_char_grammar>));
  // GIVEN THAT:
  BOOST_MPL_ASSERT ((proto::matches<proto::terminal<int>, int_grammar>));
  return 0;
}

Is this behaviour intentional?
Regards,

        Maurizio