Larry Evans wrote:
On 05/15/2006 07:49 AM, David Abrahams wrote:
Joel de Guzman <joel@boost-consulting.com> writes:
David Abrahams wrote: [snip]
Seems to me a vector can't do as well as some other structures when many of the elements of the tuple are empty classes. In terms of memory footprint? Yes.
Isn't the list<T0,T1,T2,...> memory the same as that of:
struct { T0 car; struct { T1 car; struct { T2 car; struct { ... } cdr; } cdr; } cdr; };
and the vector<T0,T1,T2,...> memory the same as that of:
struct { T0 m0; T1 m1; T2 m2; ... }
? If so, what's the reason the memory footprints would be different? If not, could you explain what is the footprint, preferably using some struct counterpart like those above?
Here's a sketch: template <class Head, class Tail> struct cons : compressed_pair<Head, Tail> { /*...*/ }; So, given empty elements such as: struct T0 {}; struct T1 {}; struct T2 {}; We'd get: struct cons { struct cons { struct cons { }; }; }; Also empty! See attached: size:1 Regards, -- Joel de Guzman http://www.boost-consulting.com http://spirit.sf.net #include <boost/compressed_pair.hpp> #include <iostream> template <class Head, class Tail = nil> struct cons : boost::compressed_pair<Head, Tail> { }; struct T0 {}; struct T1 {}; struct T2 {}; struct nil {}; int main() { std::cout << "size:" << sizeof(cons<T0, cons<T1, cons<T0, nil> > >) << std::endl; return 0; }