if (defined &top) {
    ⊤
  }
[download]

  &top if defined ⊤
[download]

You should avoid the solutions based on can for two reasons: First, they will be less efficient, and second they may have additional semantics that you don't want.

The AUTOLOAD thing is utterly ridiculous. It's like squishing a bug with a pile driver.

Edited becuase as Dominus pointed out, I was incorrect, and I wanted to disentangle my two points.

If you simply wanted to call a bunch of subroutines in order you could be more clever:

my @funcs = ();
push @funcs, 
    sub { print "middle\n"; },
    sub { print "bottom\n"; };

push @funcs, some_subroutine_that_returns_sub_refs();

foreach my $sub (@funcs) {
    &$sub;
}
[download]

By passing the subroutine references around you can do lots of powerful things without depending on global subroutine names. It all depends on what you are really trying to do.

-ben

Said knobunc:

That would work if there was a reference to the function involved. The original case had a simple subroutine definition.

OK, you're wrong, and you obviously didn't try it, or even look in the manual.

Says perlfunc:defined:

You may also use defined(&func) to check whether subroutine &func has ever been defined.

With all that code you wrote to show off, I would have thought you could also write the following three-line test to avoid embarassing yourself:

    sub a1 {} 
    print "a1 is defined\n" if defined &a1;
    print "a2 is defined\n" if defined &a2;
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#Require the file with the function definitions.
#Use eval to catch errors.
eval { require "definitions.pl"; };

#__PACKAGE__ is a token that gets replaced with the
#name of the current package. You must not quote it.
#Why? Because Perl said so.
my $package = __PACKAGE__;

#Add a 'can' test to each function call...

#This is the shortest. It uses object-oriented
#calling syntax:
top() if $package->can('top');

#If you don't like dangling if's, try this:
if ($package->can('middle')) {
    middle();
}

#This short-cuts the object-oriented calling syntax,
#and uses the relatively obscure UNIVERSAL package
#directly.
#IMO it's really messy, but it's technically the fastest.
end() if UNIVERSAL::can($package,'end');
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Hope this helps!

Jerry

Edit: chipmunk 2001-03-29

You don't need a temporary variable. Just use __PACKAGE__->can('subname')

# I know foo() and bar() exist...
# but not too sure of xyzzy() or quux()

foo();

eval { xyzzy() };
# $@ will have a value if xyzzy() isn't defined

bar();

eval { quux() };
# $@ will have a value if quux() isn't defined
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It's an anon hash that every script/package has and it contains a lot of stuff, including all functions that aren't stored like my $subo = sub {return "i am private"; };

Print it, see what develops $%^).

 
___crazyinsomniac_______________________________________
Disclaimer: Don't blame. It came from inside the void
perl -e "$q=$_;map({chr unpack qq;H*;,$_}split(q;;,q*H*));print;$q/$q;"