Gennaro Prota <gennaro_prota@yahoo.com> writes:
On Wed, 14 Apr 2004 09:34:14 +0200, Gennaro Prota <gennaro_prota@yahoo.com> wrote:
I also added the following functions: find_first, find_next, get_allocator(), max_size(), intersects() and empty().
The function intersects() was a user request. It returns true if and only if the two bitsets have any bit "in common", i.e.:
a.intersects(b) == true <=> An index i < a.size(), b.size() exists such as a[i] == true and b[i] == true
Logically, this is the same as doing (a & b).any() [except that currently a & b requires the two bitsets to have the same size - this restriction will likely be removed in the future if we reach a consensus on semantics] but is faster because it doesn't require any copy and can be done with one pass through the blocks
I was thinking, however: what about returning the index of the first bit in common (or npos), instead of true/false?
Ugh, not bit indices, at least not with *that* name! if (intersects(a,b)) // oops { } Maybe optional<std::size_t>?
Secondly, does anyone find confusing that empty() means size() == 0 rather than "the set is empty"?
Not at all. This is not a std::set<> after all. It's well known that it has the semantics of an array. But maybe you should rename it bit_array or bit_vector instead of dynamic_bitset ;-)
Someone could be tempted to write e.g.
if ((a ^ b).empty()) ...
instead of
if ((a ^ b).none()) ...
IMO if (a ^ b) should be supported. But then again, this is making me think of expression templates ;-) -- Dave Abrahams Boost Consulting http://www.boost-consulting.com