#!/uns/bin/perl
# checkargs -- check number of args in function calls
# Michael D. Ernst <mernst@csail.mit.edu>
# http://homes.cs.washington.edu/~mernst/software/checkargs.pm
# Time-stamp: <2016-10-04 10:35:20 mernst>

package checkargs;
require 5.004;			# uses "for my $var"
require Exporter;
@ISA = qw(Exporter);
@EXPORT = qw(check_args check_args_range check_args_at_least);
use strict;
use Carp;

=head1 NAME

checkargs -- Check number of args in function calls

=head1 SYNOPSIS

  use checkargs;

Then
  check_args(cArgsExpected, @_)
  check_args_range(cArgsMin, cArgsMax, @_)
  check_args_at_least(cArgsMin, @_)
where "@_" should be supplied literally.

If checkargs.pm appears in the same directory as its client, you can use:

  use FindBin ();
  use lib "$FindBin::Bin";
  use checkargs;

=head1 DESCRIPTION

checkargs checks the number of arguments passed to a perl function at run
time, catching some common errors that could otherwise go undetected until
later in the program.

As the first line of user-written subroutine foo, do one of the following:

  my ($arg1, $arg2) = check_args(2, @_);
  my ($arg1, @rest) = check_args_range(1, 4, @_);
  my ($arg1, @rest) = check_args_at_least(1, @_);
  my @args = check_args_at_least(0, @_);

These functions may also be called for side effect (put a call to one
of the functions near the beginning of the subroutine), but using the
argument checkers to set the argument list is the recommended usage.

The number of arguments and their definedness are checked; if the wrong
number are received, the program exits with an error message.

Use of checkargs is not without cost:  profiling reveals that in one
system, checkargs consumes 35% of all time.  To create a faster version of
your program after you have thoroughly tested it, name the following script
remove_check_args and run remove_check_args on the perl source to create a
faster version.  (You should probably keep around the original version,
containing the checkargs calls, for future debugging.)

  #!/uns/bin/perl -wp
  # remove_check_args -- replace check_args_.* function calls by "@_"
  # (check_args may consume 35% or more of a program's running time)
  s/^(\s*{)?\s*\bcheck_args(|_at_least|_range)\s*\(.*;/$1||""/e;
  s/=\s*\bcheck_args(|_at_least|_range)\s*\(.*;/= \@_;/;

=head1 AUTHOR

Michael D. Ernst <F<mernst@cs.washington.edu>>

=cut

## Need to check that use of caller(1) really gives desired results.
## Need to give input chunk information.
## Is this obviated by Perl 5.003's declarations?  Not entirely, I think.

sub check_args ( $@ )
{
  my ($num_formals, @args) = @_;
  if (@_ < 1) { croak "check_args needs at least 1 arg, got ", scalar(@_), ": @_\n "; }
  if ((!wantarray) && ($num_formals != 0))
    { croak "check_args called in scalar context"; }
  # Can't use croak below here: it would only go out to caller, not its caller
  my $num_actuals = @args;
  if ($num_actuals != $num_formals)
    { die error_loc() . " expected $num_formals argument",
      (($num_formals == 1) ? "" : "s"),
      ", got $num_actuals",
      (($num_actuals == 0) ? "" : ": @args"),
      "\n"; }
  for my $index (0..$#args)
    { if (!defined($args[$index]))
	{ die error_loc() . " undefined argument ", $index+1, ": @args[0..$index-1]\n"; } }
  return @args;
}

sub check_args_range ( $$@ )
{
  my ($min_formals, $max_formals, @args) = @_;
  if (@_ < 2) { croak "check_args_range needs at least 2 args, got ", scalar(@_), ": @_"; }
  if ((!wantarray) && ($max_formals != 0) && ($min_formals !=0) )
    { croak "check_args_range called in scalar context"; }
  # Can't use croak below here: it would only go out to caller, not its caller
  my $num_actuals = @args;
  if (($num_actuals < $min_formals) || ($num_actuals > $max_formals))
    { die error_loc() . " expected $min_formals-$max_formals arguments, got $num_actuals",
      ($num_actuals == 0) ? "" : ": @args", "\n"; }
  for my $index (0..$#args)
    { if (!defined($args[$index]))
	{ die error_loc() . " undefined argument ", $index+1, ": @args[0..$index-1]\n"; } }
  return @args;
}

sub check_args_at_least ( $@ )
{
  my ($min_formals, @args) = @_;
  # Don't do this, because we want every sub to start with a call to check_args*
  # if ($min_formals == 0)
  #   { die "Isn't it pointless to check for at least zero args to $subname?\n"; }
  if (scalar(@_) < 1)
    { croak "check_args_at_least needs at least 1 arg, got ", scalar(@_), ": @_"; }
  if ((!wantarray) && ($min_formals != 0))
    { croak "check_args_at_least called in scalar context"; }
  # Can't use croak below here: it would only go out to caller, not its caller
  my $num_actuals = @args;
  if ($num_actuals < $min_formals)
    { die error_loc() . " expected at least $min_formals argument",
      ($min_formals == 1) ? "" : "s",
      ", got $num_actuals",
      ($num_actuals == 0) ? "" : ": @args", "\n"; }
  for my $index (0..$#args)
    { if (!defined($args[$index]))
	{ warn error_loc() . " undefined argument ", $index+1, ": @args[0..$index-1]\n"; last; } }
  return @args;
}

sub error_loc ( ) {
  my ($pack, $file_arg, $line_arg, $subname, $hasargs, $wantarr) = caller(2);
  # Fake uses to satisfy shadowed-variables-perl: $pack $hasargs $wantarr.
  if (defined($subname))
    { return "$file_arg:$line_arg: function $subname"; }
  else
    { # One of the checkargs routines was called at top level.  That's not
      # its intended us, but make it give a good error message nonetheless.
      ($pack, $file_arg, $line_arg, $subname, $hasargs, $wantarr) = caller(1);
      return "$file_arg:$line_arg:"; }
}

1;				# successful import
__END__