Re^2: A new user question on OO Perl

Hi, Here is the get_list method in Data::Container package:

sub get_list {
    my ($self, @capwords) = @_;
    my $items = $self->{items};
    my @list = ();
    return @list unless $items;
    foreach my $item (@{$items}) {
    push @list, $item if ($item->is(@capwords));
    }
    return @list;
}
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The get_list does return an array.
Thanks for the hint you provided. I understand it now better.
One final question though. In the package Library, I have the following:

sub get_list {
    my ($self, @keywords) = @_;
    return $self->{lib}->get_list(@keywords);
}
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The method Library::get_list will actually return the result of Data::Container::getlist. Is my understanding correct?
--Jess

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Re^3: A new user question on OO Perl by chromatic (Archbishop) on Dec 19, 2007 at 08:42 UTC
As to your final question, if `$self->{lib}` contains a `Data::Container` object, then the method will return the result of the `get_list` method on that object. You could rewrite your `get_list` method to behave appropriately in scalar context with: `sub get_list { my ( $self, @capwords ) = @_; # return nothing in void context return unless defined wantarray; # return nothing if there are no items return unless $self->{items}; # return filtered list in list context return grep { $_->is( @capwords ) } @{ $self->{items} } if wantarr +ay; # return the first filtered element in scalar context for my $item ( @{ $self->{items} } ) { return $item if $item->is( @capwords ); } # explicitly return nothing if there's no filtered list return; }` [download] The important thing to learn from this is wantarray, thought you might also like to know that return with no expression returns an empty list in list context and undef in scalar context.	[reply] [d/l] [select]

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Re^3: A new user question on OO Perl
by chromatic (Archbishop) on Dec 19, 2007 at 08:42 UTC

As to your final question, if $self->{lib} contains a Data::Container object, then the method will return the result of the get_list method on that object.

You could rewrite your get_list method to behave appropriately in scalar context with:

sub get_list
{
    my ( $self, @capwords ) = @_;

    # return nothing in void context
    return unless defined wantarray;

    # return nothing if there are no items
    return unless $self->{items};

    # return filtered list in list context
    return grep { $_->is( @capwords ) } @{ $self->{items} } if wantarr
+ay;

    # return the first filtered element in scalar context
    for my $item ( @{ $self->{items} } )
    {
        return $item if $item->is( @capwords );
    }

    # explicitly return nothing if there's no filtered list
    return;
}
[download]

The important thing to learn from this is wantarray, thought you might also like to know that return with no expression returns an empty list in list context and undef in scalar context.

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