Hello friends and esteemed Monks,

This isn't a problem per-se, just something I've observed and am wondering if there's a way around it.

I am currently building several wildlife cameras that will be attached to my house and some of my cabins, each camera will be attached to a Raspberry Pi, and will stream back results to a central preview server that I will display on a television screen (up to eight inside of a single browser window).

To enhance what I've already got working, I decided that I want pan/tilt capabilities to my cameras, so for the tilt, I'm using a servo (with the servo() capability of RPi::WiringPi), and for the pan, I'm going to use a stepper motor with a ULN2003 integrated circuit, for which I'm now writing a new distribution, RPi::StepperMotor for. Everything is working great thus far, but I have a question specifically related to constant.

Normally, with a list (ie. array in this case), we can get the count of elements and assign it elsewhere:

my $array = [qw(1 2 3)];
my $array_len = @$array;

# $array_len == 3

[download]

However, in the module I'm writing, I'd prefer to use a constant:

use constant STEPPER_SEQUENCE => [
    [qw(1 0 0 1)],
    [qw(1 0 0 0)],
    [qw(1 1 0 0)],
    [qw(0 1 0 0)],
    [qw(0 1 1 0)],
    [qw(0 0 1 0)],
    [qw(0 0 1 1)],
    [qw(0 0 0 1)],
];

[download]

All is still well and great. However, what I can't seem to figure out, is how to extract the count of elements in the constant list. Here is an example. It prints only aref ok. I've tried a few things I've found in the documentation and elsewhere, but I've either overlooked something, or it's not possible to extract the info I want here:

use warnings;
use strict;
use feature 'say';

use constant STEPPER_SEQUENCE => [
    [qw(1 0 0 1)],
    [qw(1 0 0 0)],
    [qw(1 1 0 0)],
    [qw(0 1 0 0)],
    [qw(0 1 1 0)],
    [qw(0 0 1 0)],
    [qw(0 0 1 1)],
    [qw(0 0 0 1)],
];

# the below line houses the normal "ARRAY(0x...)"

use constant STEP_COUNT => STEPPER_SEQUENCE;

# ... and because STEPPER_SEQUENCE returns the "ARRAY(0x...)",
# this fails:

say "const ok" if STEPPER_SEQUENCE == 3;

my $aref = [qw(1 2 3)];

say "aref ok" if @$aref == 3;

[download]

I have tried:

@{ STEPPER_SEQUENCE }
@( STEPPER_SEQUENCE )
(STEPPER_SEQUENCE)
@STEPPER_SEQUENCE
etc, etc, etdc

[download]

Is it that I'm oblivious to something, or is what I'm attempting not possible?

Thanks!

-stevieb

In reply to [SOLVED] Get element count of CONSTANT list (aref)) by stevieb

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