How do you prevent your OO system from throwing in case a mandatory parameter is missing and convince it to return undef instead?

How do you prevent bless() from throwing in case a mandatory parameter is missing, and convince it to return undef instead?

my $data = undef;
my $object_or_undef = bless( $data, 'My::Class' );
[download]

(The above will throw an exception.)

The answer is you don't even try to stop bless bless from throwing. You wrap it in sub new { ... } so you have more control over how bless is called:

package My::Class {
  sub new {
    my ( $class, $data ) = @_;
    return undef unless ref $data eq 'HASH';
    bless $data => $class;
  }
}

my $data = undef;
my $object_or_undef = My::Class->new( $data );
[download]

Similarly, if you don't want core OO's new to throw an exception when mandatory paramaters are missing, you wrap it in another method.

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