On 03/22/08 10:29, Larry Evans wrote:
On 03/03/08 15:51, Eric Niebler wrote: [snip]
shift_right<L,R>::type is *very* simple. It is expr<tag::shift_right, args2<L, R> >. Always. It's just a 2-element container and a tag. If L and R are expressions, it is an expression. If they're grammars, it is a grammar, suitable for use as the second template parameter to proto::matches. It is simple, IMO, and leads to a very straightforward
So why is there expr<Tag,Args,Arity>::type if it's always the same as its enclosing class, expr<Tag,Args,Arity>. IIRC, mpl requires it for some metaprogramming reason, but it seems that's an implementation detail; consequently, although the user can use it, there's no need for the user to use it. If so, then why do many of the examples have:
terminal<...>::type a_term_expr={{}};
instead of just:
terminal<...> a_term_expr={{}};
? OOPS, I misread. I read "shift_right<L,R>::type is shift_right<L,R>" not "shift_right<L,R>::type is expr<tag::shift_right,args2<L,R> >". I guess I misread because shift_right<L,R> is a grammar; so, I assumed that when L and R are grammars, the expr<shift_right,args2<L,R> grammar would be shirt_right<L,R>.
Sorry.