Hello Monks,

I would like to use Attribute::Default from CPAN in order to define default arguments for subs in a easily readable way. Here is a simple example which works:

use strict;
use warnings;
use base 'Attribute::Default';
sub f : Default(undef,"xyz") {
  print("@_\nEND\n");
}
f('abc'); # 2nd argument defaults to xyz
[download]

This prints abc xyz, followed by a line saying END. Things stop to work, however, when I use Attribute::Default in a package which itself uses the Exporter; or maybe I just may some silly mistake. Here is the first thing I tried:

# This is file Co.pm
package Co;
use strict;
use warnings;
use base qw(Exporter Attribute::Default);
our @EXPORT_OK=qw(f);
sub f : Default(undef,"xyz") {
  print("@_\nEND\n");
}
1;
[download]

This will be called in the following way:

# This is file cotest.pl
use warnings;
use strict;
use Co qw(f);
f('abc');
[download]

Executing this will output just abc followed by END; i.e. the default argument is not used.

It gets even more bizarre when I handle @ISA by myself instead of letting use base doint it:

# This is file Co1.pm
package Co1;
use strict;
use warnings;
use Exporter;
use Attribute::Default;
our @ISA=qw(Exporter Attribute::Default);
our @EXPORT_OK=qw(f);
sub f : Default(undef,"xyz") {
  print("@_\nEND\n");
}
1;
[download]

I call this as usual,

# This is file cotest1.pl
use warnings;
use strict;
use Co qw(f);
f('abc');
[download]

but now I get the error message:

Invalid CODE attribute: Default(undef,"xyz") at Co1.pm
[download]

Well, I guess there is a reason why the perldoc to Attribute::Default says that you need do use base '...' to access it. Anyway, as a last resort I tried to combine the two approaches:

# This is Co2.pm
package Co2;
use strict;
use warnings;
use Exporter;
our @ISA=qw(Exporter);
use base qw(Attribute::Default);
our @EXPORT_OK=qw(f);
sub f : Default(undef,"xyz") {
  print("@_\nEND\n");
}
1;
[download]

The program for calling it is, not surprisingly:

use warnings;
use strict;
use Co2 qw(f);
f('abc');
[download]

Now I get the error message:

Can't locate object method "_ATTR_CODE_Default" via package "Co2"
[download]

What is going wrong here?

---

---

• Are you posting in the right place? Check out Where do I post X? to know for sure.
• Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:

  <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>

• Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
• Want more info? How to link or How to display code and escape characters are good places to start.