"unimport"

    no autovivification; # defaults to qw<fetch exists delete>
    no autovivification qw<fetch store exists delete>;
    no autovivification warn   => @categories;
    no autovivification strict => @categories;

Magically called when "no autovivification @opts" is encountered. Enables the features given in @opts, which can be :

• 'fetch'

  Turns off autovivification for rvalue dereferencing expressions, such as :

      $value = $arrayref->[$idx]
      $value = $hashref->{$key}
      keys %$hashref
      values %$hashref
      

  Starting from perl 5.11, it also covers "keys" and "values" on array references :

      keys @$arrayref
      values @$arrayref
      

  When the expression would have autovivified, "undef" is returned for a plain fetch, while "keys" and "values" return 0 in scalar context and the empty list in list context.

• 'exists'

  Turns off autovivification for dereferencing expressions that are parts of an "exists", such as :

      exists $arrayref->[$idx]
      exists $hashref->{$key}
      

  '' is returned when the expression would have autovivified.

• 'delete'

  Turns off autovivification for dereferencing expressions that are parts of a "delete", such as :

      delete $arrayref->[$idx]
      delete $hashref->{$key}
      

  "undef" is returned when the expression would have autovivified.

• 'store'

  Turns off autovivification for lvalue dereferencing expressions, such as :

      $arrayref->[$idx] = $value
      $hashref->{$key} = $value
      for ($arrayref->[$idx]) { ... }
      for ($hashref->{$key}) { ... }
      function($arrayref->[$idx])
      function($hashref->{$key})
      

  An exception is thrown if vivification is needed to store the value, which means that effectively you can only assign to levels that are already defined. In the example, this would require $arrayref (resp. $hashref) to already be an array (resp. hash) reference.

• 'warn'

  Emits a warning when an autovivification is avoided for the categories specified in @opts.

  Note that "no autovivification 'warn'" currently does nothing by itself, in particular it does not make the default categories warn. This behaviour may change in a future version of this pragma.

• 'strict'

  Throws an exception when an autovivification is avoided for the categories specified in @opts.

  Note that "no autovivification 'strict'" currently does nothing by itself, in particular it does not make the default categories die. This behaviour may change in a future version of this pragma.

Each call to "unimport" adds the specified features to the ones already in use in the current lexical scope.

When @opts is empty, it defaults to "qw<fetch exists delete>".

"import"

    use autovivification; # default Perl behaviour
    use autovivification qw<fetch store exists delete>;

Magically called when "use autovivification @opts" is encountered. Disables the features given in @opts, which can be the same as for "unimport".

Each call to "import" removes the specified features to the ones already in use in the current lexical scope.

When @opts is empty, it defaults to restoring the original Perl autovivification behaviour.

"A_THREADSAFE"

"A_FORKSAFE"