ShoppingCart->new(
    user => $user,
    map { $_->id => $_->quantity } @products,
);

##</code><code>##

ShoppingCart->new(
    user => $user,
    ( map { $_->id => $_->quantity } @products ),
);

##</code><code>##

use CGI;
use Data::Dumper;
my $q = CGI->new(foo => 1);
print Dumper [
    foo => $q->param('foo'),
    bar => 1,
    ];

##</code><code>##

foo => scalar $q->param('foo'),

##</code><code>##

ShoppingCart->new(
    user => $user,
    map { $_->id => $_->quantity } @products,
    bank_account => 99,
);