----- Mensaje original ----- De: "Powell, Gary" <powellg@amazon.com> Fecha: Martes, Marzo 9, 2004 10:55 pm Asunto: RE: [boost] Re: Formal Review: Circular Buffer

The VTL library does it IMO correctly, allowing that if there is an operation T1 F T2, then

V1 F V2 compiles. Otherwise you just force the user to write what should be library code.

(Obviously swap can't do this unless the Allocators are the same.)

I don't quite get you here. I think the two allocator types cannot be equal: the first allocator allocates T1's, the second T2's. I might be totally misinterpreting you, of course.

template<class T1, class T2, class Alloc> void swap( circular_buffer<T1, Alloc> &lhs, circular_buffer<T2, Alloc> &rhs) { // do an element by element swap. // and insert for the leftover elements. }

IMHO doing an elementwise swapping is very ill-behaved. It would reduce to repeatedly calling something like: template <typename T1,typename T2> void swap_different(T1& x,T1& y) { T1 tmp(y); x=y; y=x; } So, for swap to have *some* exception safety the assignment operators must not throw, which seems too restrictive (think types with dynamic allocation). Maybe things can be improved a bit with something along this line: template<class T1, class T2, class Alloc1, class Alloc2> void swap( circular_buffer<T1, Alloc1> &lhs, circular_buffer<T2, Alloc2> &rhs) { circular_buffer<T1, Alloc1> new_lhs; // copy rhs into new_lhs circular_buffer<T2, Alloc2> new_rhs; // copy lhs into new_rhs lhs.swap(new_lhs); // nothrow rhs.swap(new_rhs); // nothrow } There is a final annoyance, though: in many cases the code can emit a narrowing cast warning (if assigning an int to a short, for instance.) Joaquín M López Muñoz Telefónica, Investigación y Desarrollo