In Dancer2, what is the preferred way to keep an instance of a service-like object, that a module's routes methods can access?

Question

Imagine something along the lines of:

get( => 'hello' => sub ($app) {
    my $hello_service = $app->get_instance_of('hello_service');
    my $message = $hello_service->greet('world');
    template 'hello', {message => $message};
});

hello_service it a bit complex to initialize, I would not want to have to new it up on every request. I also don't want it to store it in package variable. Is there something in Dancer2 or some other trick that could allow me injecting services like that?

Answer 1

I like to initialize my service style classes with Bread::Board then expose them globally through a namespace like MyApp::Service, something like:

package MyApp::Service;

use Bread::Board;

# Generate service depdencencies with Bread::Board
my $c = container 'MyApp' => as {
    container 'Service' => as {
        service 'hello_service' => (
            lifecycle => 'Singleton',
            block     => sub {
                require MyApp::Service::HelloService;
                my $s = shift; # Use $s to resolve dependencies
                return MyApp::Service::HelloService->new; # Do args and stuff here
            }
        );
    };
};

no Bread::Board;

# Retrieve via MyApp::Service::hello_service
sub hello_service { return $c->resolve('Service/hello_service') }

There may be another way to do this, but this is the way I've always done it for Mojolicious, Dancer, etc. I know you mentioned not wanting to do it in a package variable (sorry).