Re: Moose: using value of one attribute in another attribute

[tobyink]

You seem to be hard-coding information about a specific battery into the battery class.

That would be like if I was trying to create a class to represent people, hard-coding my personal details as the defaults.

use 5.010;

{
    package Acpi::Info;
    use Moose;

    my @attrs = qw<
        name
        type
        online
        status
        present
        technology
        voltage_min_design
        voltage_now
        current_now
        charge_full_design
        charge_full
        charge_now
        model_name
        manufacturer
        serial_number
    >;

    for my $attr (@attrs)
    {
        has $attr => (
            is      => "ro",
            lazy    => 1,
            default => sub { my $self = shift; $self->_build($attr) }
        );
    }

    sub _build
    {
        my ($self, $key) = @_;
        my $data = $self->_data;
        $key = "POWER_SUPPLY_" . uc($key);
        $data =~ /^$key=(.+?)$/m and $1;
    }

    has file => (
        is  => "ro",
        isa => "Str",
    );

    has _data => (
        is       => "ro",
        isa      => "Str",
        lazy     => 1,
        builder  => '_build_data',
    );

    sub _build_data {
        my $self    = shift;
        local @ARGV = $self->file;
        local $/    = <ARGV>;
    }
}


# Usage
#

my $i1 = Acpi::Info->new(file => '/sys/class/power_supply/BAT1/uevent'
+);
my $i2 = Acpi::Info->new(file => '/sys/class/power_supply/ACAD/uevent'
+);

for my $supply ($i1, $i2) {
    say "----";
    for my $attr ($supply->meta->get_all_attributes) {
        my $aname = $attr->name;
        next if $aname =~ /^_/;
        say $aname, " = ", $supply->$aname;
    }
}

[mimosinnet]

Thanks very much for you clear and detailed answer! A good insight on how objects work! It is also very enlightening to understand your example on how to read the contents of the file. Also, I was not aware of the use of the underscore to make attributes and builders private!

[tobyink]

Perl doesn't have true private methods. Underscores are merely a convention to indicate that a sub is intended for internal use only.

It is possible to create do-it-yourself private subs by checking caller within a sub and then calling die if the caller is outside your module. Though this will have a performance impact if you do it a lot, and is of questionable benefit.

[zwon]

A simpler alternative to caller would be:

my $private = sub { ... };