On Wed, Dec 16, 2009 at 5:58 PM, Edward Diener <eldiener@tropicsoft.com> wrote:
Frédéric Bron wrote:
It would really be nice to have type_traits for all the possible user-defined operators.
For the moment, I am working on <, <=, >, >=, ==, !=, +, -, *, /, %. The main difficulty is to treat operators that are not defined for built-in types as a specialization is to be provided in each case. For %, I have a very long list of exceptions. When you say all operators, do you mean &&, || and bitwise operators? Can you enumerate the operators you're thinking of?
The operators which can be user-defined as specified in the C++ standard. These are given in 13.5 1, as:
new delete new[] delete[] + - * / % ˆ & | ˜ ! = < > += -= *= /= %= ˆ= &= |= << >> >>= <<= == != <= >= && || ++ -- , ->* -> () []
I personally don't need the first four for what I am working on, but it would be real nice if type_traits exrensions could discover whether any of the remaining ones are defined by the user for a particular T.
If the technique of discovering a unary operator, as given in is_incrementable in boost::detail, is known then it seems like it should work for all the unary operators. Similarly if the technique can be expanded to a single binary operator, then it seems like it should work for all the binary operators. I do understand that one technique, as given by Eric Niebler, involves a creative use of the ',' operator through overloading, it so maybe the technique would have to be modified in discovering if the ',' operator itself is overloaded for a given T.
I think, actually, if operator, is implemented for T, then the comma-operator-trick no longer works, and we can't figure out most/any of the other operators either. See http://cpp-next.com/archive/2009/10/this-week-in-boost/#more-746 Tony