G'day fionbarr,

"I've been thinking about replacing the array definition with the 'constant' definition but a little reading (on google) about using constants seems to indicate that is very little speed improvement. Opinions?"

You'd probably get a better answer if you linked to the articles you've been reading and specified what array operations you were comparing. You've really provided nothing on which to base an opinion.

Here's a fact though (from constant - CAVEATS):

"In the current version of Perl, list constants are not inlined ..." [At the time of writing, that link is for v5.18.0]

Here's timings for accessing the first element (using v5.18.0):

$ perl -Mstrict -Mwarnings -E '
    use Time::HiRes;
    use constant LABEL_ARRAY => qw(Title Section Subsection Class Cate
+gory Degree Attempt CountOfCounts);
    my @label_array = qw(Title Section Subsection Class Category Degre
+e Attempt CountOfCounts);
    my $x;
    my $t1 = Time::HiRes::time;
    $x = (LABEL_ARRAY)[0] for 1 .. 1_000_000;
    my $t2 = Time::HiRes::time;
    say $t2 - $t1;
    my $t3 = Time::HiRes::time;
    $x = (@label_array)[0] for 1 .. 1_000_000;
    my $t4 = Time::HiRes::time;
    say $t4 - $t3;
'
2.28321886062622
0.133409023284912
[download]

So, in that context, there is quite the opposite of any sort of speed improvement. Of course, while you have to access the constant array element like that (i.e. (CONSTANT)[$index]), you're more likely to access a lexical array element like this: $array[$index]

$ perl -Mstrict -Mwarnings -E '
    use Time::HiRes;
    use constant LABEL_ARRAY => qw(Title Section Subsection Class Cate
+gory Degree Attempt CountOfCounts);
    my @label_array = qw(Title Section Subsection Class Category Degre
+e Attempt CountOfCounts);
    my $x;
    my $t1 = Time::HiRes::time;
    $x = (LABEL_ARRAY)[0] for 1 .. 1_000_000;
    my $t2 = Time::HiRes::time;
    say $t2 - $t1;
    my $t3 = Time::HiRes::time;
    $x = $label_array[0] for 1 .. 1_000_000;
    my $t4 = Time::HiRes::time;
    say $t4 - $t3;
'
2.29306197166443
0.0892441272735596
[download]

So, perhaps I do have an opinion on these articles that indicate "very little speed improvement"; and that opinion would be that they are wrong. :-)

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