How Mojolicious modifies Perl syntax

Question

Reading Mojolicious minions documentation I found the following code:

use v5.28;
use Mojolicious::Lite;
use experimental qw( signatures );
use Time::HiRes qw( time );

plugin Minion => {
    SQLite => 'sqlite:' . app->home->child('minion.db'),
};

# ...
app->start;

How did they create a new syntax plugin Minion => {...}? I've never seen it in classic Perl books. Is it a function call with a hash parameter: "Minion" being a key and a hashref {...} is a value?

Also they call app->start - app is a function returning a blessed hashref? But if it was a hash why "start" is not enclosed into braces? This syntax looks strange to me.

It's not actually syntax. They're just functions with prototypes. You can read the source to see how it's done. — simbabque, Jun 07 '22 at 08:41
You could see this in [Intermediate Perl](https://www.intermediateperl.com) and the barnyard object tutorial :) — brian d foy, Jun 07 '22 at 14:35
Somewhat related https://stackoverflow.com/questions/25523983/perl-calling-methods-with-and-without-parentheses — mpapec, Jun 07 '22 at 15:44

score 6 · Accepted Answer · answered Jun 07 '22 at 09:53

app is a function which returns $app which is an instance of Mojolicious::Lite=HASH

app->start is same as app()->start

https://github.com/mojolicious/mojo/blob/24d1d1987dbfbe27eaaa37dd5db692d2deb8d07f/lib/Mojolicious/Plugin/Config.pm#L12-L14

"sub app; local *app = sub { \$app }; use Mojo::Base -strict; $content";
                             |
                             ^ not a reference but escape
                             due to eval() of double quoted string

Reproduction

perl -MMojolicious::Lite -E 'no warnings; sub foo; local *foo = sub { app }; say for foo, app'

output

Mojolicious::Lite=HASH(0xe72080)
Mojolicious::Lite=HASH(0xe72080)

plugin is a regular function

perl -MData::Dumper -wE 'sub plugin { print Dumper \@_ } plugin Minion => { SQLite => "sqlite:" }'
$VAR1 = [
          'Minion',
          {
            'SQLite' => 'sqlite:'
          }
        ];

You can add parens, and drop fat comma to look like the usual function call,

plugin("Minion", { SQLite => "sqlite:" });

How Mojolicious modifies Perl syntax

1 Answers1