# Takes a hashref, a key name, and an optional default.
# Removes that key from the hash, and returns the value or
# the default.  Blows up if there is no value or default.
sub excise_arg {
  my $args = shift;
  my $arg_name = shift;
  if (exists $args->{$arg_name}) {
    return delete $args->{$arg_name};
  }
  elsif (@_) {
    return shift;
  }
  else {
    confess("Missing required argument '$arg_name'");
  }
}

##</code><code>##

# Takes a hashref.  Verifies that it is empty
sub assert_args_done {
  my @left = keys %{ $_[0] };
  if (@left) {
    confess("Unexpected arguments '@left' left over");
  }
}

##</code><code>##

sub some_func {
  my $args = { @_ };
  my $name = excise_arg($args, 'name');       # required
  my $age = excise_arg($args, 'age', undef);  # optional
  assert_args_done($args);
  # Rest of the code here.
}