On Sun, Nov 2, 2014 at 10:14 AM, Greg London <[email protected]> wrote:
> My experience has been that having a page instance be mangled
> in some way to behave like a book is almost always going to be
> a regrettable coding decision.
>
Nice analogy. Agreed.
As to Ben's comments on Linked lists vs Perl arrays, linked lists tend to
be more flexible for insertion/deletion in the middle for highly dynamic
lists. List::Utils etc and Perl6 give us syntax to splice arrays, but
that's not efficient if doing a lot of that on truly large lists. * List
structures also the starting point for building tree structures (Tree nodes
have N of what list nodes have 1 of ... likewise the algorithms).
*(With modern CPU speeds and RAM/cache sizes, 'large' is a lot harder to
hit than it used to be, avoiding N^2, N^3, ... C^N algorithms still
sometimes matters.)
Typical ListNode structure in typed languages is a instance of a value type
and one or two pointers to the same ListNode type (one if singly linked,
but that's boring & useless), and maybe a back pointer to the owning list.
In Perl, this is typically three scalars, which may be duck-typed, with
$it->{next} and $it->{prev} being References to other ListNodes.
(N.B. Need WeakRefs for Prev and Owner references to enable garbage
collection unless list destructor runs the list breaking all links.)
Thanks to Perl's Duck Typing, how you handle the flagging of first and
last elements' prev and next can be flexibly negotiated with the algorithm
code in the node and list classes. If all code is in the List class,
$list->{first}->{prev} might be any of null (traditional), $list (acts like
a ring buffer), or $list->{first}, or some special invalid value
("Sentinel" in the literature) that is distinguishable from default null;
old Sentinel traditions were full card of "9999..99" or 0), a more OO
style would be a singleton ListSentinel instance that starts and ends every
List.
--
Bill Ricker
[email protected]
https://www.linkedin.com/in/n1vux
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