Occasionally, you might want to create a private function. A private function is one that is only available inside the scope where it was defined, private.pl:
$temp = performCalc(10, 10);
print("temp = $temp\n");
sub performCalc {
my ($firstVar, $secondVar) = @_;
my $square = sub {
return($_[0] ** 2);
};
return(&$square($firstVar) + &$square($secondVar));
};
This program prints:
temp = 200
This example is rather trivial, but it serves to show that in Perl it pays to create little helper routines. A fine line needs to be drawn between what should be included as a private function and what shouldn't. I would draw the line at 5 or 6 lines of code. Anything longer probably should be made into its own function. I would also say that a private function should have only one purpose for existence. Performing a calculation and then opening a file is too much functionality for a single private function to have.
The rest of the chapter is devoted to showing you some of the built-in functions of Perl. These little nuggets of functionality will become part of your arsenal of programming weapons.