Calling a class constructor as a function on input arguments

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

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
)
[download]

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.

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Re: Calling a class constructor as a function on input arguments by tye (Sage) on Jul 21, 2000 at 18:41 UTC
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( ... );` [download] 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}, ... );` [download]	[reply] [d/l] [select]
Re: Calling a class constructor as a function on input arguments by cwest (Friar) on Jul 21, 2000 at 18:26 UTC
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 );` [download] 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';` [download] Enjoy! -- Casey	[reply] [d/l] [select]