Re: [Boost-users] [MPL] Front of a set of types

On Mon, Aug 31, 2009 at 2:20 AM, Marco Guazzone wrote:

Dear all,

Consider this:

---[code]--- #include #include #include

#define BOOST_TEST_MODULE "boost::mpl::set tests" #define BOOST_TEST_DYN_LINK #define BOOST_TEST_MAIN #include

BOOST_AUTO_TEST_CASE( mpl_set ) {  typedef boost::mpl::set s;  BOOST_CHECK( (boost::is_same::value) );     // Test #1  BOOST_CHECK( (boost::is_same::value) );  // Test #2  BOOST_CHECK( (boost::is_same::value) );  // Test #3 } ---[/code]---

Reading the docs  http://www.boost.org/doc/libs/1_40_0/libs/mpl/doc/refmanual/set.html the "front" of a set return the first element type in s which for me is t1 So what I expect is the test to fail on tests #2 and #3 and hence to succeed on test #1

Instead the test fails on tests #1 and #2 and succeeds on test #3.

Looking inside the code I find out this is OK since a setN is defined from TN and set{N-1}, resulting in TN be the very front element

Anyway, in my opinion this is counterintuitive.

Maybe a note in the document would be helpful.

What do you think?

Thank you very much!

I do not know of set being ordered or any implementation I use (considering that runtime sets are generally hash maps), so I would not expect that to be ordered personally. I would use vector if I want something ordered.