NAME¶
Data::Structure::Util - Change nature of data within a structure
SYNOPSIS¶
use Data::Structure::Util qw(
has_utf8 utf8_off utf8_on unbless get_blessed get_refs
has_circular_ref circular_off signature
);
# get the objects in the data structure
my $objects_arrayref = get_blessed( $data );
# unbless all objects
unbless( $data );
if ( has_circular_ref( $data ) ) {
print "Removing circular ref!\n";
circular_off( $data );
}
# convert back to latin1 if needed and possible
utf8_off( $data ) if defined has_utf8( $data );
DESCRIPTION¶
"Data::Structure::Util" is a toolbox to manipulate the data inside a
data structure. It can process an entire tree and perform the operation
requested on each appropriate element.
For example: It can transform all strings within a data structure to utf8 or
transform any utf8 string back to the default encoding. It can remove the
blessing on any reference. It can collect all the objects or detect if there
is a circular reference.
It is written in C for decent speed.
FUNCTIONS¶
All Data::Structure::Util functions operate on a whole tree. If you pass them a
simple scalar then they will operate on that one scalar. However, if you pass
them a reference to a hash, array, or scalar then they will iterate though
that structure and apply the manipulation to all elements, and in turn if they
are references to hashes, arrays or scalars to all their elements and so on,
recursively.
For speed reasons all manipulations that alter the data structure do in- place
manipulation meaning that rather than returning an altered copy of the data
structure the passed data structure which has been altered.
Manipulating Data Structures¶
- has_circular_ref($ref)
- This function detects if the passed data structure has a
circular reference, that is to say if it is possible by following
references contained in the structure to return to a part of the data
structure you have already visited. Data structures that have circular
references will not be automatically reclaimed by Perl's garbage
collector.
If a circular reference is detected the function returns a reference to an
element within circuit, otherwise the function will return a false value.
If the version of perl that you are using supports weak references then any
weak references found within the data structure will not be traversed,
meaning that circular references that have had links successfully weakened
will not be returned by this function.
- circular_off($ref)
- Detects circular references in $ref (as above) and weakens
a link in each so that they can be properly garbage collected when no
external references to the data structure are left.
This means that one (or more) of the references in the data structure will
be told that the should not count towards reference counting. You should
be aware that if you later modify the data structure and leave parts of it
only 'accessible' via weakened references that those parts of the data
structure will be immediately garbage collected as the weakened references
will not be strong enough to maintain the connection on their own.
The number of references weakened is returned.
- get_refs($ref)
- Examine the data structure and return a reference to flat
array that contains one copy of every reference in the data structure you
passed.
For example:
my $foo = {
first => [ "inner", "array", { inmost => "hash" } ],
second => \"refed scalar",
};
use Data::Dumper;
# tell Data::Dumper to show nodes multiple times
$Data::Dumper::Deepcopy = 1;
print Dumper get_refs( $foo );
$VAR1 = [
{ 'inmost' => 'hash' },
[ 'inner', 'array', { 'inmost' => 'hash' } ],
\'refed scalar',
{
'first' => [ 'inner', { 'inmost' => 'hash' }, 'array' ],
'second' => \'refed scalar'
}
];
As you can see, the data structure is traversed depth first, so the top most
references should be the last elements of the array. See get_blessed($ref)
below for a similar function for blessed objects.
- signature($ref)
- Returns a md5 of the passed data structure. Any change at
all to the data structure will cause a different md5 to be returned.
The function examines the structure, addresses, value types and flags to
generate the signature, meaning that even data structures that would look
identical when dumped with Data::Dumper produce different signatures:
$ref1 = { key1 => [] };
$ref2 = $ref1;
$ref2->{key1} = [];
# this produces the same result, as they look the same
# even though they are different data structures
use Data::Dumper;
use Digest::MD5 qw(md5_hex);
print md5_hex( Dumper( $ref1 ) ), " ", md5_hex( Dumper( $ref2 ) ), "\n";
# cb55d41da284a5869a0401bb65ab74c1 cb55d41da284a5869a0401bb65ab74c1
# this produces differing results
use Data::Structure::Util qw(signature);
print signature( $ref1 ), " ", signature( $ref2 ), "\n";
# 5d20c5e81a53b2be90521167aefed9db 8b4cba2cbae0fec4bab263e9866d3911
Object Blessing¶
- unbless($ref)
- Remove the blessing from any objects found within the
passed data structure. For example:
my $foo = {
'a' => bless( { 'b' => bless( {}, "c" ), }, "d" ),
'e' => [ bless( [], "f" ), bless( [], "g" ), ]
};
use Data::Dumper;
use Data::Structure::Util qw(unbless);
print Dumper( unbless( $foo ) );
$VAR1 = {
'a' => { 'b' => {} },
'e' => [ [], [] ]
};
Note that the structure looks inside blessed objects for other objects to
unbless.
- get_blessed($ref)
- Examine the data structure and return a reference to flat
array that contains every object in the data structure you passed. For
example:
my $foo = {
'a' => bless( { 'b' => bless( {}, "c" ), }, "d" ),
'e' => [ bless( [], "f" ), bless( [], "g" ), ]
};
use Data::Dumper;
# tell Data::Dumper to show nodes multiple times
$Data::Dumper::Deepcopy = 1;
use Data::Structure::Util qw(get_blessed);
print Dumper( get_blessed( $foo ) );
$VAR1 = [
bless( {}, 'c' ),
bless( { 'b' => bless( {}, 'c' ) }, 'd' ),
bless( [], 'f' ),
bless( [], 'g' )
];
This function is essentially the same as "get_refs" but only
returns blessed objects rather than all objects. As with that function the
data structure is traversed depth first, so the top most objects should be
the last elements of the array. Note also (as shown in the above example
shows) that objects within objects are returned.
utf8 Manipulation Functions¶
These functions allow you to manipulate the state of the utf8 flags in the
scalars contained in the data structure. Information on the utf8 flag and it's
significance can be found in Encode.
- has_utf8($var)
- Returns $var if the utf8 flag is enabled for $var or any
scalar that a data structure passed in $var contains.
print "this will be printed" if defined has_utf8( "\x{1234}" );
print "this won't be printed" if defined has_utf8( "foo bar" );
Note that you should not check the truth of the return value of this
function when calling it with a single scalar as it is possible to have a
string "0" or "" for which the utf8 flag set; Since
"undef" can never have the utf8 flag set the function will never
return a defined value if the data structure does not contain a utf8
flagged scalar.
- _utf8_off($var)
- Recursively disables the utf8 flag on all scalars within
$var. This is the same the "_utf8_off" function of Encode but
applies to any string within $var. The data structure is converted
in-place, and as a convenience the passed variable is returned from the
function.
This function makes no attempt to do any character set conversion to the
strings stored in any of the scalars in the passed data structure. This
means that if perl was internally storing any character as sequence of
bytes in the utf8 encoding each byte in that sequence will then be
henceforth treated as a character in it's own right.
For example:
my $emoticons = { smile => "\x{236a}" };
use Data::Structure::Util qw(_utf8_on);
print length( $emoticons->{smile} ), "\n"; # prints 1
_utf8_off( $emoticons );
print length( $emoticons->{smile} ), "\n"; # prints 3
- _utf8_on($var)
- Recursively enables the utf8 flag on all scalars within
$var. This is the same the "_utf8_on" function of Encode but
applies to any string within $var. The data structure is converted
in-place and as a convenience the passed variable is returned from the
function.
As above, this makes no attempt to do any character set conversion meaning
that unless your string contains the valid utf8 byte sequences for the
characters you want you are in trouble. In some cases incorrect
byte sequences can segfault perl. In particular, the regular
expression engine has significant problems with invalid utf8 that has been
incorrectly marked as utf8. You should know what you are doing if you are
using this function; Consider using the Encode module as an alternative.
Contrary example to the above:
my $emoticons = { smile => "\342\230\272" };
use Data::Structure::Util qw(_utf8_on);
print length( $emoticons->{smile} ), "\n"; # prints 3
_utf8_on( $emoticons );
print length( $emoticons->{smile} ), "\n"; # prints 1
- utf8_on($var)
- This routine performs a "sv_utf8_upgrade" on each
scalar string in the passed data structure that does not have the utf8
flag turned on. This will cause the perl to change the method it uses
internally to store the string from the native encoding (normally Latin-1
unless locales come into effect) into a utf8 encoding and set the utf8
flag for that scalar. This means that single byte letters will now be
represented by multi-byte sequences. However, as long as the "use
bytes" pragma is not in effect the string will be the same length as
because as far as perl is concerned the string still contains the same
number of characters (but not bytes).
This routine is significantly different from "_utf8_on"; That
routine assumes that your string is encoded in utf8 but was marked
(wrongly) in the native encoding. This routine assumes that your string is
encoded in the native encoding and is marked that way, but you'd rather it
be encoded and marked as utf8.
- utf8_off($var)
- This routine performs a "sv_utf8_downgrade" on
each scalar string in the passed data structure that has the utf8 flag
turned on. This will cause the perl to change the method it uses
internally to store the string from the utf8 encoding into a the native
encoding (normally Latin-1 unless locales are used) and disable the utf8
flag for that scalar. This means that multiple byte sequences that
represent a single character will be replaced by one byte per character.
However, as long as the "use bytes" pragma is not in effect the
string will be the same length as because as far as perl is concerned the
string still contains the same number of characters (but not bytes).
Please note that not all strings can be converted from utf8 to the native
encoding; In the case that the utf8 character has no corresponding
character in the native encoding Perl will die with "Wide character
in subroutine entry" exception.
This routine is significantly different from "_utf8_off"; That
routine assumes that your string is encoded in utf8 and that you want to
simply mark it as being in the native encoding so that perl will treat
every byte that makes up the character sequences as a character in it's
own right in the native encoding. This routine assumes that your string is
encoded in utf8, but you want it each character that is currently
represented by multi-byte strings to be replaced by the single byte
representation of the same character.
SEE ALSO¶
Encode, Scalar::Util, Devel::Leak, Devel::LeakTrace
See the excellent article
http://www.perl.com/pub/a/2002/08/07/proxyobject.html
from Matt Sergeant for more info on circular references.
The development version of this module and others can be found at
http://opensource.fotango.com/svn/trunk/Data-Structure-Util/
BUGS¶
"signature()" is sensitive to the hash randomisation algorithm
This module only recurses through basic hashes, lists and scalar references. It
doesn't attempt anything more complicated.
THANKS TO¶
James Duncan and Arthur Bergman who helped me and found a name for this module.
Leon Brocard and Richard Clamp have provided invaluable help to debug this
module. Mark Fowler rewrote large chunks of the documentation and patched a
few bugs.
AUTHOR¶
This release by Andy Armstrong <andy@hexten.net>
Originally by Pierre Denis <pdenis@fotango.com>
http://opensource.fotango.com/
COPYRIGHT¶
Copyright 2003, 2004 Fotango - All Rights Reserved.
This module is released under the same license as Perl itself.