On Sat, Dec 11, 2004 at 09:00:05AM -0500, David Abrahams wrote:
Another note : filter_iterator's complexity may not match the requirements of iterators (increment in constant time amortized), depending on the predicate's behavior.
That's a tricky question, which is why it's been left unanswered. You might look at it this way: for any filter and sequence of length N there are some constant number of elements M that will pass the filter. If the cost of traversing the unfiltered sequence is O(N) then so is the cost of traversing the filtered sequence. But N/M is a constant, so it's also N/M O(M) and therefore also O(M).
But N/M does not have to be bounded by a constant when N grows.
Is that stretching the definition of an iterator? I'm not sure.
That's too much for me. I tend to think that it's stretching what users might expect when they see "constant time amortized operation". -- Sylvain