On Monday, 28 September 2020 at 19:18:20 UTC, H. S. Teoh wrote:
On Mon, Sep 28, 2020 at 05:18:41PM +0000, ikod via
Digitalmars-d-learn wrote:
On Monday, 28 September 2020 at 14:58:15 UTC, Steven
Schveighoffer wrote:
[...]
> One could write a specific function to iterate and remove. I
This looks like dead end to me, as you may not only remove
items from arbitrary positions while iterating over
collection, but also insert items. Also this can happens not
only inside foreach body, but in other kinds of iteration. And
also there can be nested iterations over same collection.
The problem with arbitrary, unrestricted modification of a
container while iterating over it, is that it inevitably leads
to counterintuitive results.
Thanks for your reply, and sorry if I was not clear, but I meant
AA. AA is unordered container, so for me intuitive behavior for
mutations visibility during iteration is next:
1) you must not see removed keys. Let our keys are (unordered) A
D C E F, you stay on D and remove E. Then E must not be seen on
any future iteration steps.
2) you may or may not see any inserted keys. As AA is unordered
container there is no reason to expect anything about position of
key you just inserted - it can fall before or after current
iteration position, so implementation is free to show inserted
keys or not. I prefer not to see new keys.
3) you expect to visit all not removed keys exactly once.
Is it sane?
For example, suppose you have a container containing the
elements A, B, C, D, E, and you're iterating over it in that
order.
1) Suppose you're at element C, and you decide that you need to
insert F. Then there's the question: should F be included in
...
2) Suppose you're at element C, and you decide to delete D.
"Obviously", the current iteration should not include D. Or
...
Sure, everything you said is correct for ordered collection.
Also, what if the act of deleting D requires an internal
reorganization of the container? If this reorg changes the
iteration order, how should the current iteration proceed?
Intuitive behavior should follow mentioned three rules regardless
of internal implementation.
