my $obj = new Foo;

This syntax introduces weird parser ambiguities that often depend on the order of compilation. Stick with Foo->new().

When it works, it is. The problem is that it doesn't always work. new Foo has two barewords, and whenever the Perl parser encounters barewords, it has to guess at what they are. Sometimes it has hints at what those barewords are (if it's encountered declarations of filehandles or subroutines) and it can guess correctly. Sometimes it doesn't have hints, because Perl embraces late binding.

Sometimes it has hints which contradict late binding altogether. There's where you run into problems, because you have to know exactly which hints matter and when the parser knows about them to diagnose and correct the problem.

Alternately, you could use a syntax which isn't ambiguous to the parser and has the benefit of clarifying what exactly happens (new not being a keyword in Perl as it is in some other languages with OO systems).

I don't think there's any guessing. If there is, let me know so I can fix this.

To expand a bit on what chromatic said:

The key words in "method invocation using the METHOD CLASS_OR_INSTANCE LIST form is exactly equivalent to CLASS_OR_INSTANCE->METHOD (LIST) form." are "method invocation".

In other words, if new Foo is resolved by the perl parser as a method call it is exactly equivalent. The problem is that it isn't always. For instance, this works:

#!/usr/bin/perl
use warnings;
use strict;

my $a = new Foo;

$a->hello;

package Foo;
sub new {
    return bless {},shift;
}

sub hello {
    print "hello";
}
[download]

output:

hello
[download]

While this doesn't:

#!/usr/bin/perl
use warnings;
use strict;

sub new {
    print "haha";
    return;
}

my $a = new Foo;

$a->hello;

package Foo;
sub new {
    return bless {},shift;
}

sub hello {
    print "hello";
}
[download]

output:

Bareword "Foo" not allowed while "strict subs" in use at test.pl line 
+10.
Execution of test.pl aborted due to compilation errors.
[download]

"What should it profit a man, if he should win a flame war, yet lose his cool?"

Ahh, interesting. I have never shot myself in the foot with that caliber of bullet. Thank you for elucidating.

Is there some way to do this:


#!/usr/bin/perl
use warnings;
use strict;
use Foo; # some "forward declaration" syntax instead of looking for Fo
+o.pm?

sub new {
    print "haha";
    return;
}

my $a = new Foo;

$a->hello;

package Foo;
sub new {
    return bless {},shift;
}

sub hello {
    print "hello";
}
[download]

I couldn't find it under use in perlfunc. I was also trying use main::Foo; and use ::Foo; based on some ideas that popped into my head while reading about Packages in perlmod.

---

I humbly seek wisdom.

Avoiding the:

my $obj = new Foo;
[download]

indirect object syntax is routine Perl style advice. See, for example:
• Perl Best Practices section 15.12 "Don't use the indirect object syntax"
• Perl Cookbook chapter 13, "A Warning on Indirect Object Notation" section