Question

I have a subroutine called debug I use in my code. It basically allows me to see what’s going on, etc.

sub debug {
    my $message      = shift;
    my $messageLevel = shift;

    our $debugLevel;
    $messageLevel = 1 if not defined $messageLevel;
    return if $messageLevel > $debugLevel;
    my $printMessage = "    " x $messageLevel . "DEBUG: $message\n";
    print STDERR $printMessage;
    return $printMessage;
}

I want to prototype this, so I can do things like this:

debug "Here I am! And the value of foo is $foo";

or

debug "I am in subroutine foo", 3;

At the same time, I like putting subroutine definitions at the bottom of my program, so you don’t have to wade 1/2 way through the code to find the meat of the program.

I’d like to do this:

sub debug($;$);  #Prototype debug subroutine

/Here goes the main program code/

sub debug {      #The entire subroutine goes here
   /Here goes the debug subroutine code/
}

However, I get a warning when I do this:

Prototype mismatch: sub main::debug ($;$) vs none at foo.pl line 249.

So, I’m stuck putting the prototype definition in both places. What is the correct way to do something like this?

---

RESPONSE

Stop! Module time. – Chris Lutz

A module? You mean create a separate file? That adds a bit of complication without solving the issue I’m trying to solve: Removing the need for parentheses around this particular subroutine.

our $debugLevel; should not be in the sub body anyway, but I agree with Chris on this. – Sinan Ünür 3 hours ago

The our $debugLevel does not have to be there in this case, but if I defined a class and I want to use this subroutine in my class for debugging, I need it. I can put it in my class as ::debug

Surprisingly, Far more than everything you ever wanted to know about prototypes in Perl doesn’t address this, but I believe you cannot avoid writing the prototype in both places.

I was hoping for an easy way to avoid it. There is a way as Eric Strom showed. Unfortunately, it’s longer than my debug routine.

I used to use prototypes, but I’ve developed the habit of not writing separate declarations for subroutines and using parentheses on all calls: debug(“I am in subroutine foo”, 3);. It’s been suggested that prototypes really aren’t a good idea. TMTOWTDI – Keith Thompson 3 hours

Except I’ll tend to do:

debug (qq(The value of Foo is "$foo"), 3);

which can be less clear when reading, and can be a pain to type. Whenever you double up parenthese, you’re asking for trouble. The last thing I want to do is debug my debug statements.

Why do you want prototypes? See this question How to pass optional parameters to a Perl function – TLP

Yes, there are lots of problems with prototyping. The main problem is that it simply doesn’t do what people think it should do: Declare the variable types for the parameters you’re passing to your function.

This is not the reason I’m using prototyping here.

I rarely use prototypes. In fact, this is probably the only case in all of my code where I do.

Answer 1

Just get rid of prototypes altogether:

sub debug;

debug "Here I am! And the value of foo is $foo";
debug "I am in subroutine foo", 3;

sub debug {
    # body of debug
}