Calling a class constructor as a function on input arguments

[princepawn]

Often one knows beforehand which subclass of base class in which to initialize one's method. However, in my case, I want to call a constructor as a function of the operating system that I am on. My first thought was to use a hash keyed on operating system name and store a reference to the new of each class as the value, ie:

%constructor = (
  'MSWin32' => \&FTP::Session::Win32->new,
  'HPUX'    => \&FTP::Session::HPUX->new
)

Which brings up an additional question: since I am using an arrow in the above code instead of ::, will the first argument to the new be the package name? And will it only pass arguments if I had used ::? Thanks for any help guys.

[tye]

This sounds like a job for anonymous subs:

    my %constructor= {
        MSWin32 => sub { FTP::Session::Win32->new( @_ ) },
        HPUX => sub { FTP::Session::HPUX->new( @_ ) },
    }
    my $ctor= $constructor{$^O};
    die "No constructor for $^O"   if  ! $ctor;
    my $session= $ctor->( ... );
    # Old Perl requires:  $session= &$ctor( ... );

The next best thing is UNIVERSAL::can(), which returns a reference to a named method. But then you need to cache each class name so that you can pass that in to the sub that you got a reference to:

    my %class= {
        MSWin32 => "FTP::Session::Win32",
        HPUX => "FTP::Session::HPUX",
    }
    my %constructor= {
        MSWin32 => FTP::Session::Win32->can("new"),
        HPUX => FTP::Session::HPUX->can( "new" ),
    }
    my $ctor= $constructor{$^O};
    die "No constructor for $^O"   if  ! $ctor;
    my $session= $ctor->( $class{$^O}, ... );
    # Old Perl requires:  $session= &$ctor( $class{$^O}, ... );

[cwest]

I need more info about the context of the code you're going to write.

However, here's a possible solution:

my $os = eval "\\&FTP::Session::${^O}->new";
my %constor = ( $^O => $os );

I'm pretty sure that's what you're looking for.

Yes, the first argument is the package name, that's why constructors could look like this:

sub new { bless {}, shift };
# which is equivalent to this
sub new {
  my $class = shift @_;
  my $self  = {};
  my $ref   = bless $self, $class;
  return $ref;
}
# Bless could actually be:
bless {}, 'Package::Name';

Enjoy!

--
Casey