no autovivification;
my $hashref;
my $a = $hashref->{key_a}; # $hashref stays undef
if (exists $hashref->{option}) { # Still undef
...
}
delete $hashref->{old}; # Still undef again
$hashref->{new} = $value; # Vivifies to { new => $value }
This pragma lets you disable autovivification for some constructs and optionally throws a warning or an error when it would have happened.
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 :
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.
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.
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.
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. $hashref) to already be an array (resp. hash) reference.
Emits a warning when an autovivification is avoided for the categories specified in @opts.
Note that "no autovivification 'warn'" currently does nothing by itself, in particular it does not make the default categories warn. This behaviour may change in a future version of this pragma.
Throws an exception when an autovivification is avoided for the categories specified in @opts.
Note that "no autovivification 'strict'" currently does nothing by itself, in particular it does not make the default categories die. This behaviour may change in a future version of this pragma.
Each call to "unimport" adds the specified features to the ones already in use in the current lexical scope.
When @opts is empty, it defaults to "qw<fetch exists delete>".
use autovivification; # default Perl behaviour
use autovivification qw<fetch store exists delete>;
Magically called when "use autovivification @opts" is encountered. Disables the features given in @opts, which can be the same as for ``unimport''.
Each call to "import" removes the specified features to the ones already in use in the current lexical scope.
When @opts is empty, it defaults to restoring the original Perl autovivification behaviour.
The pragma doesn't apply when one dereferences the returned value of an array or hash slice, as in "@array[$id]->{member}" or @hash{$key}->{member}. This syntax is valid Perl, yet it is discouraged as the slice is here useless since the dereferencing enforces scalar context. If warnings are turned on, Perl will complain about one-element slices.
Autovivifications that happen in code "eval"'d during the global destruction phase of a spawned thread or pseudo-fork (the processes used internally for the "fork" emulation on Windows) are not reported.
A C compiler. This module may happen to build with a C++ compiler as well, but don't rely on it, as no guarantee is made in this regard.
XSLoader (standard since perl 5.6.0).
You can contact me by mail or on "irc.perl.org" (vincent).
perldoc autovivification
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.