subroutine introspection

[misterb101]

Hi fellow Perl mates, I am working on a big application using ExtJS as a front-end. The interface communicates with the backend using Ext::Direct, a JSON API. What I am trying to do is create the API specification automatically. The API basically requires 2 things. specify which subroutines are made accessible and how many parameters they take, which I am solving like this:

sub foo($$) : Direct {
    ...
}

The subroutine attribute is not a problem, but I can't seem to figure out how I can list how many arguments the subroutine requires:

my $numArgs = GiveMeTheNumberOfRequiredArgumentsOf(\&foo);

can anyone implement the 'GiveMeTheNumberOfRequiredArgumentsOf' subroutine for me ;) ? THANKS

[JavaFan]

You can get the prototype of a function as:

prototype \&foo;

I leave it up to you to parse the prototype (which has been enhanced in recent Perl versions).

[misterb101]

I have been programming Perl for 15 years... and I never knew this amazingly simple function.... Thanks for enlightening me :D

[ikegami]

Do you want the minimum number of arguments that must be specified, or the miminum number of arguments that must be passed to the function?

# Minimum number of arguments that must be specified = 0
# Miminum number of arguments that must be passed    = 1
sub f(_) {}

# Minimum number of arguments that must be specified
sub get_min_require_params {
   my ($sub) = @_;
   my $required_params = 0;
   my $prototype = prototype($sub);
   return 0 if !defined($prototype);
   for ($prototype) {
      if (/
         \G
         (?: \$
         |   \*
         |   \\(?: \[ [^\]] \] | [^\[] )
         |   \&
         )
      /xsgc) {
         ++$required_params;
         next;
      }

      if (/
         \G
         (?: \_   # Can only be followed by ";"
         |   \@
         |   \%
         |   \;
         |   \z
      /xsgc) {
         last;
      }

      die("Unrecognized prototype\n");
   }
}

To get the minimum number of arguments that must be passed to the function, you'll need to move "_" to the top "if".

I don't see how either version is useful, so I'm sure there's an XY problem lurking.

perlsub (for info on prototypes), prototype