Re: [Boost-users] [mpl] insert not inserting?

JOAQUIN LOPEZ MU?Z wrote:

I think you want to write

mpl::end<Constraints>::type

Thanks for the suggestion, but it doesn't change the behavior of the program: the result of the insertion of a new element into the two-element set is a new set with only two elements (one of the original elements is lost). Please try it and see if you get the same thing I do.

Well, excuse me if the following is obvious to you, but ::type is to a metafunction what actual invocation is to a run-time function. So, mpl::end<Constraints> refers to the name of the entity, but does not actually compute its "return value" unless you add the ::type suffix.

I don't think this always holds. For example, I don't need to add the ::type suffix when I make a typedef or when I do an assertion: typedef mpl::set MySet; BOOST_MPL_ASSERT(( mpl::equal, mpl::set > )); Until this thread, I figured I could wallow in ignorance about when ::type was needed and when not, because I assumed that if I got it wrong, the code would not compile. (Sort of the way a lot of people think about const...) Now I know better, sigh. Scott