Objects in Perl (part 2,352)
February 20, 2009 by Glen. Filed under perl, programming.
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 `@_` 
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