On 12/23/2004 11:16 AM, David Abrahams wrote: [snip]
Another is that (unless you use nonstandard language extensions) only flat structures allow O(1) random access.
I'm afraid I don't understand. By "access" do you mean access to the elements in the structure? If so, then I don't understand why: r.factor<TypeMap,Index>::my_field where r is the tuple and Index is the field number (or the superclass number), is not O(1) access. Could you explain why? BTW, if the method used in sum is slightly changed (replace max with + when calculating max_size), then the storage can all be moved to the most derived class and all superclasses just contain functions; hence, the padding problem (I guess) is not longer there. This, of course, is at the cost of a little more complicated product::project method.