1Data::Structure::Util(3U)ser Contributed Perl DocumentatiDoanta::Structure::Util(3)
2
6 Data::Structure::Util - Change nature of data within a structure
7
9 use Data::Structure::Util qw(
10 has_utf8 utf8_off utf8_on unbless get_blessed get_refs
11 has_circular_ref circular_off signature
12 );
13 # get the objects in the data structure
15 my $objects_arrayref = get_blessed( $data );
16 # unbless all objects
18 unbless( $data );
19 if ( has_circular_ref( $data ) ) {
21 print "Removing circular ref!\n";
22 circular_off( $data );
23 }
24 # convert back to latin1 if needed and possible
26 utf8_off( $data ) if defined has_utf8( $data );
27
29 "Data::Structure::Util" is a toolbox to manipulate the data inside a
30 data structure. It can process an entire tree and perform the operation
31 requested on each appropriate element.
32 For example: It can transform all strings within a data structure to
34 utf8 or transform any utf8 string back to the default encoding. It can
35 remove the blessing on any reference. It can collect all the objects or
36 detect if there is a circular reference.
37 It is written in C for decent speed.
39
41 All Data::Structure::Util functions operate on a whole tree. If you
42 pass them a simple scalar then they will operate on that one scalar.
43 However, if you pass them a reference to a hash, array, or scalar then
44 they will iterate though that structure and apply the manipulation to
45 all elements, and in turn if they are references to hashes, arrays or
46 scalars to all their elements and so on, recursively.
47 For speed reasons all manipulations that alter the data structure do
49 in- place manipulation meaning that rather than returning an altered
50 copy of the data structure the passed data structure which has been
51 altered.
52 Manipulating Data Structures
54 has_circular_ref($ref)
55 This function detects if the passed data structure has a circular
56 reference, that is to say if it is possible by following references
57 contained in the structure to return to a part of the data
58 structure you have already visited. Data structures that have
59 circular references will not be automatically reclaimed by Perl's
60 garbage collector.
61 If a circular reference is detected the function returns a
63 reference to an element within circuit, otherwise the function will
64 return a false value.
65 If the version of perl that you are using supports weak references
67 then any weak references found within the data structure will not
68 be traversed, meaning that circular references that have had links
69 successfully weakened will not be returned by this function.
70 circular_off($ref)
72 Detects circular references in $ref (as above) and weakens a link
73 in each so that they can be properly garbage collected when no
74 external references to the data structure are left.
75 This means that one (or more) of the references in the data
77 structure will be told that the should not count towards reference
78 counting. You should be aware that if you later modify the data
79 structure and leave parts of it only 'accessible' via weakened
80 references that those parts of the data structure will be
81 immediately garbage collected as the weakened references will not
82 be strong enough to maintain the connection on their own.
83 The number of references weakened is returned.
85 get_refs($ref)
87 Examine the data structure and return a reference to flat array
88 that contains one copy of every reference in the data structure you
89 passed.
90 For example:
92 my $foo = {
94 first => [ "inner", "array", { inmost => "hash" } ],
95 second => \"refed scalar",
96 };
97 use Data::Dumper;
99 # tell Data::Dumper to show nodes multiple times
100 $Data::Dumper::Deepcopy = 1;
101 print Dumper get_refs( $foo );
102 $VAR1 = [
104 { 'inmost' => 'hash' },
105 [ 'inner', 'array', { 'inmost' => 'hash' } ],
106 \'refed scalar',
107 {
108 'first' => [ 'inner', { 'inmost' => 'hash' }, 'array' ],
109 'second' => \'refed scalar'
110 }
111 ];
112 As you can see, the data structure is traversed depth first, so the
114 top most references should be the last elements of the array. See
115 get_blessed($ref) below for a similar function for blessed objects.
116 signature($ref)
118 Returns a md5 of the passed data structure. Any change at all to
119 the data structure will cause a different md5 to be returned.
120 The function examines the structure, addresses, value types and
122 flags to generate the signature, meaning that even data structures
123 that would look identical when dumped with Data::Dumper produce
124 different signatures:
125 $ref1 = { key1 => [] };
127 $ref2 = $ref1;
129 $ref2->{key1} = [];
130 # this produces the same result, as they look the same
132 # even though they are different data structures
133 use Data::Dumper;
134 use Digest::MD5 qw(md5_hex);
135 print md5_hex( Dumper( $ref1 ) ), " ", md5_hex( Dumper( $ref2 ) ), "\n";
136 # cb55d41da284a5869a0401bb65ab74c1 cb55d41da284a5869a0401bb65ab74c1
137 # this produces differing results
139 use Data::Structure::Util qw(signature);
140 print signature( $ref1 ), " ", signature( $ref2 ), "\n";
141 # 5d20c5e81a53b2be90521167aefed9db 8b4cba2cbae0fec4bab263e9866d3911
142 Object Blessing
144 unbless($ref)
145 Remove the blessing from any objects found within the passed data
146 structure. For example:
147 my $foo = {
149 'a' => bless( { 'b' => bless( {}, "c" ), }, "d" ),
150 'e' => [ bless( [], "f" ), bless( [], "g" ), ]
151 };
152 use Data::Dumper;
154 use Data::Structure::Util qw(unbless);
155 print Dumper( unbless( $foo ) );
156 $VAR1 = {
158 'a' => { 'b' => {} },
159 'e' => [ [], [] ]
160 };
161 Note that the structure looks inside blessed objects for other
163 objects to unbless.
164 get_blessed($ref)
166 Examine the data structure and return a reference to flat array
167 that contains every object in the data structure you passed. For
168 example:
169 my $foo = {
171 'a' => bless( { 'b' => bless( {}, "c" ), }, "d" ),
172 'e' => [ bless( [], "f" ), bless( [], "g" ), ]
173 };
174 use Data::Dumper;
176 # tell Data::Dumper to show nodes multiple times
177 $Data::Dumper::Deepcopy = 1;
178 use Data::Structure::Util qw(get_blessed);
179 print Dumper( get_blessed( $foo ) );
180 $VAR1 = [
182 bless( {}, 'c' ),
183 bless( { 'b' => bless( {}, 'c' ) }, 'd' ),
184 bless( [], 'f' ),
185 bless( [], 'g' )
186 ];
187 This function is essentially the same as "get_refs" but only
189 returns blessed objects rather than all objects. As with that
190 function the data structure is traversed depth first, so the top
191 most objects should be the last elements of the array. Note also
192 (as shown in the above example shows) that objects within objects
193 are returned.
194 utf8 Manipulation Functions
196 These functions allow you to manipulate the state of the utf8 flags in
197 the scalars contained in the data structure. Information on the utf8
198 flag and it's significance can be found in Encode.
199 has_utf8($var)
201 Returns $var if the utf8 flag is enabled for $var or any scalar
202 that a data structure passed in $var contains.
203 print "this will be printed" if defined has_utf8( "\x{1234}" );
205 print "this won't be printed" if defined has_utf8( "foo bar" );
206 Note that you should not check the truth of the return value of
208 this function when calling it with a single scalar as it is
209 possible to have a string "0" or "" for which the utf8 flag set;
210 Since "undef" can never have the utf8 flag set the function will
211 never return a defined value if the data structure does not contain
212 a utf8 flagged scalar.
213 _utf8_off($var)
215 Recursively disables the utf8 flag on all scalars within $var.
216 This is the same the "_utf8_off" function of Encode but applies to
217 any string within $var. The data structure is converted in-place,
218 and as a convenience the passed variable is returned from the
219 function.
220 This function makes no attempt to do any character set conversion
222 to the strings stored in any of the scalars in the passed data
223 structure. This means that if perl was internally storing any
224 character as sequence of bytes in the utf8 encoding each byte in
225 that sequence will then be henceforth treated as a character in
226 it's own right.
227 For example:
229 my $emoticons = { smile => "\x{236a}" };
231 use Data::Structure::Util qw(_utf8_on);
232 print length( $emoticons->{smile} ), "\n"; # prints 1
233 _utf8_off( $emoticons );
234 print length( $emoticons->{smile} ), "\n"; # prints 3
235 _utf8_on($var)
237 Recursively enables the utf8 flag on all scalars within $var. This
238 is the same the "_utf8_on" function of Encode but applies to any
239 string within $var. The data structure is converted in-place and as
240 a convenience the passed variable is returned from the function.
241 As above, this makes no attempt to do any character set conversion
243 meaning that unless your string contains the valid utf8 byte
244 sequences for the characters you want you are in trouble. In some
245 cases incorrect byte sequences can segfault perl. In particular,
246 the regular expression engine has significant problems with invalid
247 utf8 that has been incorrectly marked as utf8. You should know
248 what you are doing if you are using this function; Consider using
249 the Encode module as an alternative.
250 Contrary example to the above:
252 my $emoticons = { smile => "\342\230\272" };
254 use Data::Structure::Util qw(_utf8_on);
255 print length( $emoticons->{smile} ), "\n"; # prints 3
256 _utf8_on( $emoticons );
257 print length( $emoticons->{smile} ), "\n"; # prints 1
258 utf8_on($var)
260 This routine performs a "sv_utf8_upgrade" on each scalar string in
261 the passed data structure that does not have the utf8 flag turned
262 on. This will cause the perl to change the method it uses
263 internally to store the string from the native encoding (normally
264 Latin-1 unless locales come into effect) into a utf8 encoding and
265 set the utf8 flag for that scalar. This means that single byte
266 letters will now be represented by multi-byte sequences. However,
267 as long as the "use bytes" pragma is not in effect the string will
268 be the same length as because as far as perl is concerned the
269 string still contains the same number of characters (but not
270 bytes).
271 This routine is significantly different from "_utf8_on"; That
273 routine assumes that your string is encoded in utf8 but was marked
274 (wrongly) in the native encoding. This routine assumes that your
275 string is encoded in the native encoding and is marked that way,
276 but you'd rather it be encoded and marked as utf8.
277 utf8_off($var)
279 This routine performs a "sv_utf8_downgrade" on each scalar string
280 in the passed data structure that has the utf8 flag turned on.
281 This will cause the perl to change the method it uses internally to
282 store the string from the utf8 encoding into a the native encoding
283 (normally Latin-1 unless locales are used) and disable the utf8
284 flag for that scalar. This means that multiple byte sequences that
285 represent a single character will be replaced by one byte per
286 character. However, as long as the "use bytes" pragma is not in
287 effect the string will be the same length as because as far as perl
288 is concerned the string still contains the same number of
289 characters (but not bytes).
290 Please note that not all strings can be converted from utf8 to the
292 native encoding; In the case that the utf8 character has no
293 corresponding character in the native encoding Perl will die with
294 "Wide character in subroutine entry" exception.
295 This routine is significantly different from "_utf8_off"; That
297 routine assumes that your string is encoded in utf8 and that you
298 want to simply mark it as being in the native encoding so that perl
299 will treat every byte that makes up the character sequences as a
300 character in it's own right in the native encoding. This routine
301 assumes that your string is encoded in utf8, but you want it each
302 character that is currently represented by multi-byte strings to be
303 replaced by the single byte representation of the same character.
304
306 Encode, Scalar::Util, Devel::Leak, Devel::LeakTrace
307 See the excellent article
309 http://www.perl.com/pub/a/2002/08/07/proxyobject.html from Matt
310 Sergeant for more info on circular references.
311
313 https://github.com/AndyA/Data--Structure--Util
314
316 "signature()" is sensitive to the hash randomisation algorithm
317 This module only recurses through basic hashes, lists and scalar
319 references. It doesn't attempt anything more complicated.
320
322 James Duncan and Arthur Bergman who helped me and found a name for this
323 module. Leon Brocard and Richard Clamp have provided invaluable help
324 to debug this module. Mark Fowler rewrote large chunks of the
325 documentation and patched a few bugs.
326
328 This release by Andy Armstrong <andy@hexten.net>
329 Originally by Pierre Denis <pdenis@fotango.com>
331 http://opensource.fotango.com/
333
335 Copyright 2003, 2004 Fotango - All Rights Reserved.
336 This module is released under the same license as Perl itself.
338perl v5.32.0 2020-07-28 Data::Structure::Util(3)