autovivification - Lexically disable autovivification.
VERSION
- Version 0.05
+ Version 0.18
SYNOPSIS
no autovivification;
When an undefined variable is dereferenced, it gets silently upgraded to
an array or hash reference (depending of the type of the dereferencing).
This behaviour is called *autovivification* and usually does what you
- mean (e.g. when you store a value) but it's sometimes unnatural or
- surprising because your variables gets populated behind your back. This
- is especially true when several levels of dereferencing are involved, in
+ mean (e.g. when you store a value) but it may be unnatural or surprising
+ because your variables gets populated behind your back. This is
+ especially true when several levels of dereferencing are involved, in
which case all levels are vivified up to the last, or when it happens in
intuitively read-only constructs like "exists".
optionally throws a warning or an error when it would have happened.
METHODS
- "unimport @opts"
- Magically called when "no autovivification" is encountered. Enables the
- features given in @opts, which can be :
+ "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'
- Turn off autovivification for rvalue dereferencing expressions, such
- as "$value = $hashref->{key}[$idx]{$field}", "keys
- %{$hashref->{key}}" or "values %{$hashref->{key}}". Starting from
- perl 5.11, it also covers "keys" and "values" on array references.
+ 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'
- Turn off autovivification for dereferencing expressions that are
- parts of an "exists", such as "exists
- $hashref->{key}[$idx]{$field}". '' is returned when the expression
- would have autovivified.
+ 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'
- Turn off autovivification for dereferencing expressions that are
- parts of a "delete", such as "delete $hashref->{key}[$idx]{$field}".
+ 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'
- Turn off autovivification for lvalue dereferencing expressions, such
- as "$hashref->{key}[$idx]{$field} = $value" or "for
- ($hashref->{key}[$idx]{$field}) { ... }". 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 "$hashref->{key}[$idx]" to
- already be a hash reference).
+ 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'
- Emit a warning when an autovivification is avoided.
+ 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'
- Throw an exception when an autovivification is avoided.
+ 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/".
+ When @opts is empty, it defaults to "qw<fetch exists delete>".
- "import @opts"
- Magically called when "use autovivification" is encountered. Disables
- the features given in @opts, which can be the same as for "unimport".
+ "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.
+CONSTANTS
+ "A_THREADSAFE"
+ True if and only if the module could have been built with thread-safety
+ features enabled. This constant only has a meaning when your perl is
+ threaded, otherwise it will always be false.
+
+ "A_FORKSAFE"
+ True if and only if this module could have been built with fork-safety
+ features enabled. This constant will always be true, except on Windows
+ where it is false for perl 5.10.0 and below.
+
CAVEATS
+ Using this pragma will cause a slight global slowdown of any subsequent
+ compilation phase that happens anywere in your code - even outside of
+ the scope of use of "no autovivification" - which may become noticeable
+ if you rely heavily on numerous calls to "eval STRING".
+
The pragma doesn't apply when one dereferences the returned value of an
array or hash slice, as in "@array[$id]->{member}" or
- @hash{$key}->{member}. This syntax is valid Perl, yet it's discouraged
+ @hash{$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.
+
DEPENDENCIES
- perl 5.8.
+ perl 5.8.3.
- XSLoader (standard since perl 5.006).
+ 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).
SEE ALSO
perlref.
perldoc autovivification
- Tests code coverage report is available at
- <http://www.profvince.com/perl/cover/autovivification>.
-
ACKNOWLEDGEMENTS
Matt S. Trout asked for it.
COPYRIGHT & LICENSE
- Copyright 2009,2010 Vincent Pit, all rights reserved.
+ Copyright 2009,2010,2011,2012,2013,2014,2015,2017 Vincent Pit, all
+ rights reserved.
This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
projects / perl / modules / autovivification.git / blobdiff