On Fri, 08 May 2009 11:57:41 -0400, Walter Bright
<newshou...@digitalmars.com> wrote:
Steven Schveighoffer wrote:
You still have not addressed the usage of iterators as general data
structure pointers. As far as I can tell, ranges do not implement this.
i.e. find surrounding elements of an element.
With iterators:
auto iter = container.find(elem);
auto elembefore = iter - 1;
auto elemafter = iter + 1;
Assuming incrementing and decrementing an iterator is checked for
out-of-bounds.
The problem is that last statement - "Assuming". If the iterator is the
first or the last, or if there's only 1 or 2 elements in the container,
it's crash city. Iterators are *inherently* uncheckable.
For finding the elemafter, it's trivial as find() returns a range from
the found element to the end (and it's also trivially checkable!).
For elembefore, there's a bit more work involved, probably defining a
find() that returns a range backed up by one one.
You're assuming an iterator does not know its bounds. Maybe I should call
it something other than iterator. How about cursor?
There are definite reasons to use containers in ways that don't involve
std.algorithm, where something that has the easy ability to move back and
forth N times without weird subrange operations.
I'm thinking of a structure with either a pointer to the container for
bounds checking, or a range and pointer combined (where the invariant is
that the pointer is always within the range).
I'm not saying ranges are not great, i think they are a HUGE step forward,
but the statement "Iterators must be eliminated" may be too harsh.
Perhaps the unchecked iterator, yes (but you may want to allow it in
certain performance-critical code).
-Steve
