On 11.03.2011 12:53, Thomas Jarosch wrote:

Hello,

here's a small boost::logic::tribool riddle:

-<snip>-------------------------------------

#include<iostream> #include<boost/logic/tribool.hpp>

int main(void) { boost::logic::tribool foo(boost::logic::indeterminate); if (foo != true) { std::cout<< "reached1\n"; }

if (foo == boost::logic::indeterminate) { std::cout<< "reached2\n"; }

return 0; }

-<snap>-------------------------------------

Try to determine the printed result without looking at the boost::logic::tribool implementation / documentation.

Intuitive? If you see tribool as a type that can have the three distinct values "true", "false", and "indeterminate", then no, it's not intuitive. If you instead see tribool as having the two values "true" and "false" and in addition the state "indeterminate", which means "could be true or false, not sure", then the result of the comparison operators is intuitive, but the way they behave in conditions still isn't.

Sebastian

On Fri, Mar 11, 2011 at 11:53 AM, Thomas Jarosch < thomas.jarosch@intra2net.com> wrote:

Hello,

here's a small boost::logic::tribool riddle:

-<snip>-------------------------------------

#include <iostream> #include <boost/logic/tribool.hpp>

int main(void) { boost::logic::tribool foo(boost::logic::indeterminate); if (foo != true) { std::cout << "reached1\n"; }

if (foo == boost::logic::indeterminate) { std::cout << "reached2\n"; }

return 0; }

-<snap>-------------------------------------

Try to determine the printed result without looking at the boost::logic::tribool implementation / documentation.

Intuitive?

Ok, I guessed, got it wrong, read the docs, and still don't get it! Modifying your example to... #include <iostream> #include <boost/logic/tribool.hpp> int main(void) { boost::logic::tribool foo(boost::logic::indeterminate); if (foo != true) { std::cout << "reached1\n"; } if (foo == boost::logic::indeterminate) { std::cout << "reached2\n"; } if (boost::logic::indeterminate == boost::logic::indeterminate) { std::cout << "reached3\n"; } return 0; } only prints "reached3", so I can see the logic of second test being indeterminate rather than true, but then surely the comparing indeterminate with indeterminate should also be true? Weird! - Rob.