Perl Best Practices [Electronic resources] نسخه متنی

16.10. Coercions

Specify coercions as :STRINGIFY, :NUMERIFY, and :BOOLIFY methods .

In addition to the :ATTR markers for attribute hashes, Class::Std also supplies markers for subroutines that implement conversions to numbers, strings, and booleans:

sub count : NUMERIFY {    
# Call count( ) method whenever object used as number

my ($self, $ident) = @_;
return scalar @{ $elements_of{$ident} };
}
sub as_str : STRINGIFY {  
# Call as_str( ) method whenever object used as string

my ($self, $ident) = @_;
return sprintf '(%s)', join $COMMA, @{ $elements_of{$ident} };
}
sub is_okay : BOOLIFY {   
# Call is_okay( ) method whenever object used as boolean

my ($self) = @_;
return !$self->Houston_We_Have_A_Problem( );
} 

This provides a simpler, more convenient, and less repetitive interface than use overload:

sub count {
my ($self) = @_;
return scalar @{ $elements_of{ident $self} };
}
sub as_str {
my ($self) = @_;
return sprintf '(%s)', join $COMMA, @{ $elements_of{ident $self} };
}
sub is_okay {
my ($self) = @_;
return !$self->Houston_We_Have_A_Problem( );
}
use overload (
q{0+}   => 'count',
q{"}   => 'as_str',
q{bool} => 'is_okay',
fallback => 1,
);