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Posted by ZeldorBlat on 05/19/07 03:10
On May 18, 10:44 pm, Jerry Stuckle <jstuck...@attglobal.net> wrote:
> ZeldorBlat wrote:
> > On May 18, 9:05 pm, Jerry Stuckle <jstuck...@attglobal.net> wrote:
> >> ZeldorBlat wrote:
> >>> On May 18, 11:40 am, "Jon Slaughter" <Jon_Slaugh...@Hotmail.com>
> >>> wrote:
> >>>> "ZeldorBlat" <zeldorb...@gmail.com> wrote in message
> >>>>news:1179501018.125313.63600@p77g2000hsh.googlegroups.com...
> >>>>> On May 18, 11:05 am, "Jon Slaughter" <Jon_Slaugh...@Hotmail.com>
> >>>>> wrote:
> >>>>>> Is it safe to remove elements from an array that foreach is working on?
> >>>>>> (normally this is not the case but not sure in php) If so is there an
> >>>>>> efficient way to handle it? (I could add the indexes to a temp array and
> >>>>>> delete afterwards if necessary but since I'm actually working in a nested
> >>>>>> situation this could get a little messy. I guess I could set there values
> >>>>>> to
> >>>>>> null and remove them afterwards?
> >>>>>> Thanks,
> >>>>>> Jon
> >>>>> Why don't you try it and see what happens?
> >>>> Um... cause I did... but that doesn't mean much. Just cause someone tries
> >>>> something doesn't prove that it will always work like that...
> >>>> got any more bright ideas?
> >>>> Or is the question to hard for you?
> >>> No, the question is not to (sic) hard for me. But, as you've already
> >>> discovered, it isn't that difficult to test, either.
> >> Sorry, I agree with Jon on this one.
>
> >> I make it a habit not to delete entries in a foreach() loop. Rather, I
> >> build an array of keys I want to delete, and after the loop ends, delete
> >> the entries from my delete array.
>
> >> I don't know whether an operation like this is guaranteed to work in PHP
> >> - I've never seen it documented, so I suspect not. And just because it
> >> works in one release under a certain set of conditions is not a
> >> guarantee it will work on another release or under different conditions.
>
> >> --
> >> ==================
> >> Remove the "x" from my email address
> >> Jerry Stuckle
> >> JDS Computer Training Corp.
> >> jstuck...@attglobal.net
> >> ==================
>
> > I never said I disagreed with him -- in fact I, too, generally don't
> > delete elements inside a foreach. However, I will say that when I
> > have done it things seem to work as expected. I guess it all comes
> > down to whether or not the array's internal pointer is modified when
> > you unset the element it's pointing to (I suspect it isn't).
>
> > I see a lot of questions in these newsgroups that look something like,
> > "What happens if I do X?" or "In PHP is this code valid?" The point I
> > was trying to make (and apparently Jon took offense to it) was that
> > it's easy enough to just try it and see what happens. Software is
> > just that: soft. It can be changed easily enough :)
>
> Yes, and in a case like this that change can break his code.
>
> As I said - I've never seen it documented that this is valid. Maybe it
> is and I missed it; I really don't know.
>
> But this isn't the same as a lot of other "try it and find out"
> questions. In this case it's a known problem in other programming
> languages, and if it is documented that this should or should not work,
> no one has pointed anyone to it.
>
> And until I see something from the PHP developers saying it is OK, I
> wouldn't do it.
>
> --
> ==================
> Remove the "x" from my email address
> Jerry Stuckle
> JDS Computer Training Corp.
> jstuck...@attglobal.net
> ==================
This suggests that it's safe (from <http://www.php.net/foreach>):
"Unless the array is referenced, foreach operates on a copy of the
specified array and not the array itself. Therefore, the array pointer
is not modified as with the each() construct, and changes to the array
element returned are not reflected in the original array."
So unsetting a value in the original array should not affect the copy
that foreach is working on.
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