Learning Perl Objects, References, and Modules

Chapter 6. Subroutine References

So far, you’ve seen references to arrays and hashes. You can also take a reference to a subroutine (sometimes called a coderef).

Why would you want to do that? Well, in the same way that taking a reference to an array lets you have the same code work on different arrays at different times, taking a reference to a subroutine allows the same code to call different subroutines at different times. Also, references permit complex data structures. A reference to a subroutine allows a subroutine to effectively become part of that complex data structure.

Put another way, a variable or a complex data structure is a repository of values throughout the program. A reference to a subroutine can be thought of as a repository of behavior in a program. The examples in this section show how this works.

Referencing a Named Subroutine

The Skipper and Gilligan are having a conversation:

sub skipper_greets {
  my $person = shift;
  print "Skipper: Hey there, $person!\n";
}

sub gilligan_greets {
  my $person = shift;
  if ($person eq "Skipper") {
    print "Gilligan: Sir, yes, sir, $person!\n";
  } else {
    print "Gilligan: Hi, $person!\n";
  }
}

skipper_greets("Gilligan");
gilligan_greets("Skipper");

This results in:

Skipper: Hey there, Gilligan!
Gilligan: Sir, yes, sir, Skipper!

So far, nothing unusual has happened. Note however that Gilligan has two different behaviors, depending on whether he’s addressing the Skipper or someone else.

Now, have the Professor walk into the hut. Both of ...