Using sub routines or AUTOLOAD for XS constants

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

Having switched to Sub::Exporter from Exporter, I came across functionality differences. If one of your sub routine names is not defined, Sub::Exporter croaks where as Exporter does not export that name.

Currently I have a number of constants that get AUTOLOADed through:

# This AUTOLOAD is used to 'autoload' constants from the constant() XS
+ function.
sub AUTOLOAD {
    my $constname;
    our $AUTOLOAD;
    ($constname = $AUTOLOAD) =~ s/.*:://;
    croak "&Blah::constant not defined" if $constname eq 'constant';
    my ($error, $val) = constant($constname);
    if ($error) { croak $error; }
    {
        no strict 'refs';
        *$AUTOLOAD = sub { $val };
    }
    goto &$AUTOLOAD;
}
[download]

(this being the standard h2xs boilerplate code).

Is it better practice to setup 1 sub routine for each constant such as:

foreach my $constname (@constants) {
    {
        no strict 'refs';
        *$constname = sub {
            use strict;
            my ($error, $val) = constant($constname);
            if ($error) { croak $error; }
            return $val;
          }
    }
}
[download]

for Sub::Exporter?

The only downside I can see is the added code overhead, but not having AUTOLOAD around seems like a win.

Comment on Using sub routines or AUTOLOAD for XS constants Select or Download Code

Replies are listed 'Best First'.
Re: Using sub routines or AUTOLOAD for XS constants by chromatic (Archbishop) on Jan 01, 2010 at 20:23 UTC
If you're getting the error message `"can't locate exported subroutine $name via $class"` from Sub::Exporter's `default_generator()`, the best option is to override `can()` in your package when you use `AUTOLOAD()`. That's a good practice anyway, though. I haven't tested this code, but something like this should work: `sub can { my ($class, $name) = @_; return if $name eq 'constant'; my ($error, $val) = constant($name); return if $error; my $sub = sub () { $val }; { no strict 'refs'; *{ $class . '::' . $name } = $sub; } return $sub; }` [download]	[reply] [d/l] [select]
Re^2: Using sub routines or AUTOLOAD for XS constants by ikegami (Patriarch) on Jan 01, 2010 at 22:23 UTC
Sub::Exporter uses `can`? That's a bug. `can` is for methods, and it makes no sense to export methods.	[reply] [d/l] [select]
Re^3: Using sub routines or AUTOLOAD for XS constants by chromatic (Archbishop) on Jan 02, 2010 at 10:25 UTC
`can` is for methods... I agree in principle, but what's the difference in practice between a method and a function, at least when you're groveling through a package's symbol table? There's likely a bug lurking in Sub::Exporter here as well, if it ever tries to export an inherited function.	[reply] [d/l]
Re^4: Using sub routines or AUTOLOAD for XS constants by ikegami (Patriarch) on Jan 02, 2010 at 19:55 UTC
Re^2: Using sub routines or AUTOLOAD for XS constants by aflott (Beadle) on Jan 01, 2010 at 20:54 UTC
Yes that is exactly what I was looking for. Although I had to add `return \&{$class . '::' . $name} if (defined(&{$name}));` for having the non-constant subs reachable. Thanks for the nudge in the right direction.	[reply] [d/l]