Allegedly the solution to a common headache I had recently: save control points to a curve path where order of insertion is important - shape depends on it. But also delete a control point in the middle of the path (by key): meaning retain insertion order and at the same time search/insert/delete O(1) by key ... hmmm

kikuchiyo please prepare a test case to prove your hack's worth (especially when memory is not large - as others here said already).

Here is a thought:

#!/usr/bin/perl

use strict;
use warnings;
use feature qw/say/;

my %hoh = (
    foo => { value => 'second', time => time},
    bar => { value => 'first', time => time},
    baz => { value => 'third', time => time},
);

for my $elem (sort {$a->{time} <=> $b->{time}} values %hoh) {
    say "value => " . $elem->{value};
}
[download]

which does not work because time() granularity is too thick/un-fine. Using DateTime::HiRes is not a guarantee either.

Should one be using instruction-based counting?

Perhaps Perl has a monotonically increasing counter, sort of like an incrementing-only program counter/instruction pointer? Alas, even than can not guarantee one instruction to insert only one hash element (can it?).

A very interesting problem which has solutions but not EFFICIENT solutions. This is one of the most ingenious I have seen.

bw, bliako