One of my issues with Perl has always been its implementation of OOP. Or, to be precise, the multitude of ways that a class can be declared (blessed hash, inside-out, Class::Std etc). I would argue that this is a case where TMTOWTDI is not advantageous. Enter Piers Cawley and his _Moose for Ruby Programmers_ talk at the London.pm Technical Meeting, 20th February 2009. MooseX::Declare is yet another way, but check this out…
use MooseX::Declare;
class BankAccount {
has 'balance' => ( isa => 'Num', is => 'rw', default => 0 );
method deposit (Num $amount) {
$self->balance( $self->balance + $amount );
}
method withdraw (Num $amount) {
my $current_balance = $self->balance();
( $current_balance >= $amount )
|| confess "Account overdrawn";
$self->balance( $current_balance - $amount );
}
}
class CheckingAccount extends BankAccount {
has 'overdraft_account' => ( isa => 'BankAccount', is => 'rw' );
before withdraw (Num $amount) {
my $overdraft_amount = $amount - $self->balance();
if ( $self->overdraft_account && $overdraft_amount > 0 ) {
$self->overdraft_account->withdraw($overdraft_amount);
$self->deposit($overdraft_amount);
}
}
}
Firstly, yes, that is indeed Perl. Secondly, wow: it actually _looks_ like a class definition. And this was the big win for me, as anyone coming from a Java or PHP background will find it trivial to understand what’s going on here. The main point is that by using MooseX::Declare, you are moving towards a more declarative programming style describing _what_ the program should do rather than _how_ it should achieve it. So, no more unrolling `@_` 