MoobX - Reactive programming framework heavily inspired by JavaScript's MobX


version 0.1.0


    use 5.20.0;

    use MoobX;

    my $first_name :Observable;
    my $last_name  :Observable;
    my $title      :Observable;

    my $address = observer {
        join ' ', $title || $first_name, $last_name;

    say $address;  # nothing

    $first_name = "Yanick";
    $last_name  = "Champoux";

    say $address;  # Yanick Champoux

    $title = 'Dread Lord';

    say $address;  # Dread Lord Champoux


As I was learning how to use|MobX, I thought it'd be fun to try to implement something similar in Perl. So I did.

To set Moose object attributes to be observers or observables, take a gander at MoobX::Trait::Observable and MoobX::Trait::Observer.

To have an idea of the mechanics of MoobX, see the two blog entries in the SEE ALSO section.

This is also the early stages of life for this module. Consider everythign as alpha quality, and the API still subject to huge changes.


The module automatically exports 3 functions: observer, observable and autorun.


    observable my $foo;
    observable my @bar;
    observable my %quux;

Marks the variable as an observable, i.e. a variable which value can be watched by observers, which will be updated when it changes.

Under the hood, the variable is tied to the relevant MoobX::TYPE class MoobX::TYPE::Observable role.

If you want to declare the variable, assign it a value and set it as observable, there are a few good ways to do it, and one bad:

    my $foo = 3;
    observable $foo;            # good

    observable( my $foo = 3 );  # good

    observable my $foo;         # good
    $foo = 3;

    observable my $foo = 3;     # bad

That last one doesn't work because Perl parses it as observable( my $foo ) = 3, and assigning values to non lvalueed functions don't work.

Or, better, simply use the :Observable attribute when you define the variable.

    my $foo :Observable = 2;
    my @bar :Observable = 1..10;
    my %baz :Observable = ( a => 1, b => 2 );


    observable my $quantity;
    observable my $price;

    my $total = observer {
        $quantity * $price

    $quantity = 2;
    $price = 6.00;

    print $total; # 12

Creates a MoobX::Observer object. The value returned by the object will react to change to any observable values within its definition.

Observers are lazy, meaning that they compute or recompute their values when they are accessed. If you want them to eagerly recompute their values, autorun is what you want.

If an observer function is run and doesn't report any dependency, it'll emit the warning 'MoobX observer doesn't observe anything', because chances are there's something weird going on. The warning can be silenced via the global variable $MoobX::WARN_NO_DEPS.

    my $foo :Observable;

    my $debugging = 0;

    # if $debugging == 1, we'd get a warning
    local $MoobX::WARN_NO_DEPS = 0;

    my $spy = observer {
        return unless $debugging;

        say $foo;


    observable my $foo;

    autorun {
        say "\$foo is now $foo";

    $foo = 1; # prints '$foo is now 1'

    $foo = 2; # prints '$foo is now 2'

Like observer, but immediatly recompute its value when its observable dependencies change.

SEE ALSO|MobX - the original inspiration and - the two blog entries that introduced MobX.


Yanick Champoux <>


This software is copyright (c) 2017 by Yanick Champoux.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.