on Thu Apr 09 2009, Larry Evans <cppljevans-AT-suddenlink.net> wrote:
On 04/08/09 10:35, David Abrahams wrote:
on Sun Apr 05 2009, Larry Evans <cppljevans-AT-suddenlink.net> wrote:
Just as the ForwardPredicate is "augmented" with protection against dereferencing the end<numbers>::type in this code:
https://svn.boost.org/trac/boost/browser/trunk/boost/mpl/iter_fold_if.hpp#L4...
shouldn't the BackwardPredicate also be augmented with the same protection here:
https://svn.boost.org/trac/boost/browser/trunk/boost/mpl/iter_fold_if.hpp#L7...
Well, it doesn't need to be; if it did, tests and uses wouldn't compile ;-)
Just think about how you'd implement it and it should become obvious why.
David,
With the change shown in attachment, the mpl tests passsed, as shown in the vault's:
Of course it does. The change has no effect, because the predicate is never executed on the past-the-end position. When recursing inward, you need to terminate recursion when you reach the end *or* when the forward predicate is satisfied, and you can't test the forward predicate on the past-the-end position. When recursing outward, the backward predicate simply tells you whether to keep applying the operation or not; whether you'll evaluate the predicate on a past-the-end position is a non-issue. -- Dave Abrahams BoostPro Computing http://www.boostpro.com