Storing references to constructors with context

pernod has asked for the wisdom of the Perl Monks concerning the following question:

I am trying to create a hash of references for use in a factory-methodish subroutine. My idea is as follows:

my %constructors = ( "one" => \One->new,
                     "two" => \Two->new );

sub factorish {
    my ( $type, @arguments ) = @_;

    my $consref = $constructors{ $type }
        or die "No handler for $type.";

    return $consref -> ( @arguments );
}
[download]

This does not compile, from the obvious reason that I don't have references in the hash. The reason I don't want to use

my %constructors = ( "one" => \&One::new,
                     "two" => \&Two::new );
[download]

is that I will then have to explicitly fournish the package name in the factorish function, which defeats my cunning ploy of making an elegant function for choosing constructors.

A possible solution is to change the keys in the hash to the class name, and use this when calling the constructor:

my %constructors = ( "One" => \&One::new,
                     "Two" => \&Two::new );

sub factorish {
    my ( $type, @arguments ) = @_;

    my $consref = $constructors{ $type }
        or die "No handler for $type.";

    return $consref -> ( $type, @arguments );
}
[download]

This is fine, but in cases where I don't know (nor care, for that matter) about the class name, this will not work. Am I trying something that is not possible, or is there a way around this?

pernod
--
Mischief. Mayhem. Soap.

Comment on Storing references to constructors with context Select or Download Code

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Re: Storing references to constructors with context by broquaint (Abbot) on Jul 10, 2003 at 15:39 UTC
Or you could not bother with the references at all and just use a simple class method constructor e.g `my %constructors = ( One => 'new', Two => 'new', ); sub factorish { my ( $type, @arguments ) = @_; die "No handler for $type." unless exists $constructors{ $type } and my $method = $constructors{ $type }; return $type->$method( @arguments ); }` [download] So the `%constructors` hash will consist of the class names and the method names of the constructors, simple as that :) HTH `_________ broquaint`	[reply] [d/l]
Re: Storing references to constructors with context by Jenda (Abbot) on Jul 10, 2003 at 21:04 UTC
You want this: `my %constructors = ( "one" => sub {One->new(@_)}, "two" => sub {Two->new(@_)} );` [download] Jenda Always code as if the guy who ends up maintaining your code will be a violent psychopath who knows where you live. -- Rick Osborne Edit by castaway: Closed small tag in signature	[reply] [d/l]