TSa Thomas.Sandlass-at-vts-systems.de |Perl 6| wrote:
Since Larry said that single assignment semantics is the ideal
we should strive for, I would opt for the iterator being unaffected
by the assignment to @a. When this happens the singly assigned
former content of @a is snaphot by the iterator.
That's what my C++ vararray class does with iterators. That way they
don't go stale if you manipulate the array during iteration.
Iterators are independent objects in Perl 6 that can be used in other
ways. I think it vaguly specifies in the synopses that the for loop
will use the default iterator for that List, provided by a member for
that purpose.
You can have different iterator types that work in different ways. You
can create which ever kind you need for the purpose.
The synopses does not specify the details of iterators. But you can
logically deduce that the default iterator needs to provide for rw (not
ref?) binding, since the for loop is documented to do that, if the for
loop uses the default iterator. The meta-law is that things work like
in Perl 5 unless specified otherwise, so the for loop needs to continue
to track the changing contents of the List object.
But I imagine you can create an iterator with various options: snapshot
or tracking, rw, readonly, or ref, and other attributes.
So if you really wanted to depend on those semantics, you could write
something like
my $it = @a.iterator(:snapshot);
while =$it -> { body-of-loop }
You could allow adverbs on the 'for' loop to pass through to the call to
iterator(), but that is probably too much syntactic sugar for the value
it gives.
--John
