Over time, modules in Perl can become obsolete, or superseded by newer modules.  Furthermore, despite being over 15 years old, Perl 5 continues to grow. Much of this growth comes from Perl's practice of assimilating popular CPAN modules into the core language. Modules that are not part of the core Perl language must be explicitly included to be used by a program, but modules that are part of the core language need not be. When a module has been assimilated into the core language, the original module is still available in CPAN.

Modules that have become obsolete, superseded by newer modules, or integrated into the core language are considered deprecated. Do not import deprecated modules.

If a module becomes deprecated because its features have been integrated into the core language, then their features may be used without importing the deprecated module.

Here is a list of CPAN modules that should be considered deprecated, according to Perl::Critic.

Noncompliant Code Example (Universal::can())

This noncompliant code example tries to see if an object supports a method. The Universal::can() method provides this capability. It was formerly an external CPAN module, but it is now part of Perl itself.

use UNIVERSAL qw(can);  # deprecated

# ...

sub doit {
  my ($func) = @_;

  if (can($self, $func)) {
    $self->$func();
  }
  # ...
}

Although this code works correctly now, the use statement will be rejected by the Perl interpreter someday.

Compliant Solution

This compliant solution uses Universal::can() without explicitly importing it.

# use UNIVERSAL qw(can);  # deprecated

# ...

sub doit {
  my ($func) = @_;

  if ($self->can($func)) {
    $self->$func();
  }
  # ...
}

Risk Assessment

Using deprecated or obsolete classes or methods in program code can lead to erroneous behavior.

Automated Detection

Bibliography