optional o<size_t>. x<(size_t)0 is different to x<0

[harris.pc@…]

This is a very subtle but key bug. Comparing slightly different types changes the way the comparison is done.

#include <boost/optional.hpp>
#include <cassert>

int main()
{
   boost::optional<size_t> x;
   assert((x < (size_t)0) == (x < 0));
   return 0;
}

result:

$ g++ -g -I boost_1_64_0/ -o test_optional-d test_optional.cpp
$ ./test_optional-d
$ test_optional.cpp:7: int main(): Assertion `(x < (size_t)0) == (x < 0)' failed.

I am scared to think what this might affect in my code...

---

I would actually prefer to turn off the implicit cast in operator<(), and only allow : optional<T> < optional<T>

I'd rather it throw a compile error and instead force me to do something like if (x && *x < 0)

Because I do not always thing 'none' should be 'less than' anything. It should not be comparable.

[harris.pc@…]

Note that I am using gcc 4.8.4 MSVC 2010 doesn't allow (x < 0) to compile, complaining about the types not matching.