[loeg]

I think my complaints are summed up nicely in some of your coauthors' report:

http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1967.htm

(1) runtime constraint handler callbacks are a terrible API.

(2) The additional boilerplate doesn't buy us anything — the user can still specify the wrong size.

(3) The Annex invents a feature out of whole cloth, rather than standardizing existing practices. There are no performant real-world implementations that anyone uses. Microsoft's similar functionality is non-standard.