1version::Internals(3) User Contributed Perl Documentationversion::Internals(3)
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NAME

6       version::Internals - Perl extension for Version Objects
7

DESCRIPTION

9       Overloaded version objects for all modern versions of Perl.  This
10       documents the internal data representation and underlying code for
11       version.pm.  See version.pod for daily usage.  This document is only
12       useful for users interested in the gory details.
13

WHAT IS A VERSION?

15       For the purposes of this module, a version "number" is a sequence of
16       positive integer values separated by one or more decimal points and
17       optionally a single underscore.  This corresponds to what Perl itself
18       uses for a version, as well as extending the "version as number" that
19       is discussed in the various editions of the Camel book.
20
21       There are actually two distinct kinds of version objects:
22
23       Decimal versions
24           Any version which "looks like a number", see "Decimal Versions".
25           This also includes versions with a single decimal point and a
26           single embedded underscore, see "Alpha Versions", even though these
27           must be quoted to preserve the underscore formatting.
28
29       Dotted-Decimal versions
30           Also referred to as "Dotted-Integer", these contains more than one
31           decimal point and may have an optional embedded underscore, see
32           Dotted-Decimal Versions.  This is what is commonly used in most
33           open source software as the "external" version (the one used as
34           part of the tag or tarfile name).  A leading 'v' character is now
35           required and will warn if it missing.
36
37       Both of these methods will produce similar version objects, in that the
38       default stringification will yield the version "Normal Form" only if
39       required:
40
41         $v  = version->new(1.002);     # 1.002, but compares like 1.2.0
42         $v  = version->new(1.002003);  # 1.002003
43         $v2 = version->new("v1.2.3");  # v1.2.3
44
45       In specific, version numbers initialized as "Decimal Versions" will
46       stringify as they were originally created (i.e. the same string that
47       was passed to "new()".  Version numbers initialized as "Dotted-Decimal
48       Versions" will be stringified as "Normal Form".
49
50   Decimal Versions
51       These correspond to historical versions of Perl itself prior to 5.6.0,
52       as well as all other modules which follow the Camel rules for the
53       $VERSION scalar.  A Decimal version is initialized with what looks like
54       a floating point number.  Leading zeros are significant and trailing
55       zeros are implied so that a minimum of three places is maintained
56       between subversions.  What this means is that any subversion (digits to
57       the right of the decimal place) that contains less than three digits
58       will have trailing zeros added to make up the difference, but only for
59       purposes of comparison with other version objects.  For example:
60
61                                          # Prints     Equivalent to
62         $v = version->new(      1.2);    # 1.2        v1.200.0
63         $v = version->new(     1.02);    # 1.02       v1.20.0
64         $v = version->new(    1.002);    # 1.002      v1.2.0
65         $v = version->new(   1.0023);    # 1.0023     v1.2.300
66         $v = version->new(  1.00203);    # 1.00203    v1.2.30
67         $v = version->new( 1.002003);    # 1.002003   v1.2.3
68
69       All of the preceding examples are true whether or not the input value
70       is quoted.  The important feature is that the input value contains only
71       a single decimal.  See also "Alpha Versions".
72
73       IMPORTANT NOTE: As shown above, if your Decimal version contains more
74       than 3 significant digits after the decimal place, it will be split on
75       each multiple of 3, so 1.0003 is equivalent to v1.0.300, due to the
76       need to remain compatible with Perl's own 5.005_03 == 5.5.30
77       interpretation.  Any trailing zeros are ignored for mathematical
78       comparison purposes.
79
80   Dotted-Decimal Versions
81       These are the newest form of versions, and correspond to Perl's own
82       version style beginning with 5.6.0.  Starting with Perl 5.10.0, and
83       most likely Perl 6, this is likely to be the preferred form.  This
84       method normally requires that the input parameter be quoted, although
85       Perl's after 5.8.1 can use v-strings as a special form of quoting, but
86       this is highly discouraged.
87
88       Unlike "Decimal Versions", Dotted-Decimal Versions have more than a
89       single decimal point, e.g.:
90
91                                          # Prints
92         $v = version->new( "v1.200");    # v1.200.0
93         $v = version->new("v1.20.0");    # v1.20.0
94         $v = qv("v1.2.3");               # v1.2.3
95         $v = qv("1.2.3");                # v1.2.3
96         $v = qv("1.20");                 # v1.20.0
97
98       In general, Dotted-Decimal Versions permit the greatest amount of
99       freedom to specify a version, whereas Decimal Versions enforce a
100       certain uniformity.
101
102       Just like "Decimal Versions", Dotted-Decimal Versions can be used as
103       "Alpha Versions".
104
105   Alpha Versions
106       For module authors using CPAN, the convention has been to note unstable
107       releases with an underscore in the version string. (See CPAN.)
108       version.pm follows this convention and alpha releases will test as
109       being newer than the more recent stable release, and less than the next
110       stable release.  Only the last element may be separated by an
111       underscore:
112
113         # Declaring
114         use version 0.77; our $VERSION = version->declare("v1.2_3");
115
116         # Parsing
117         $v1 = version->parse("v1.2_3");
118         $v1 = version->parse("1.002_003");
119
120       Note that you must quote the version when writing an alpha Decimal
121       version.  The stringified form of Decimal versions will always be the
122       same string that was used to initialize the version object.
123
124   Regular Expressions for Version Parsing
125       A formalized definition of the legal forms for version strings is
126       included in the "version::regex" class.  Primitives are included for
127       common elements, although they are scoped to the file so they are
128       useful for reference purposes only.  There are two publicly accessible
129       scalars that can be used in other code (not exported):
130
131       $version::LAX
132           This regexp covers all of the legal forms allowed under the current
133           version string parser.  This is not to say that all of these forms
134           are recommended, and some of them can only be used when quoted.
135
136           For dotted decimals:
137
138               v1.2
139               1.2345.6
140               v1.23_4
141
142           The leading 'v' is optional if two or more decimals appear.  If
143           only a single decimal is included, then the leading 'v' is required
144           to trigger the dotted-decimal parsing.  A leading zero is
145           permitted, though not recommended except when quoted, because of
146           the risk that Perl will treat the number as octal.  A trailing
147           underscore plus one or more digits denotes an alpha or development
148           release (and must be quoted to be parsed properly).
149
150           For decimal versions:
151
152               1
153               1.2345
154               1.2345_01
155
156           an integer portion, an optional decimal point, and optionally one
157           or more digits to the right of the decimal are all required.  A
158           trailing underscore is permitted and a leading zero is permitted.
159           Just like the lax dotted-decimal version, quoting the values is
160           required for alpha/development forms to be parsed correctly.
161
162       $version::STRICT
163           This regexp covers a much more limited set of formats and
164           constitutes the best practices for initializing version objects.
165           Whether you choose to employ decimal or dotted-decimal for is a
166           personal preference however.
167
168           v1.234.5
169               For dotted-decimal versions, a leading 'v' is required, with
170               three or more sub-versions of no more than three digits.  A
171               leading 0 (zero) before the first sub-version (in the above
172               example, '1') is also prohibited.
173
174           2.3456
175               For decimal versions, an integer portion (no leading 0), a
176               decimal point, and one or more digits to the right of the
177               decimal are all required.
178
179       Both of the provided scalars are already compiled as regular
180       expressions and do not contain either anchors or implicit groupings, so
181       they can be included in your own regular expressions freely.  For
182       example, consider the following code:
183
184               ($pkg, $ver) =~ /
185                       ^[ \t]*
186                       use [ \t]+($PKGNAME)
187                       (?:[ \t]+($version::STRICT))?
188                       [ \t]*;
189               /x;
190
191       This would match a line of the form:
192
193               use Foo::Bar::Baz v1.2.3;       # legal only in Perl 5.8.1+
194
195       where $PKGNAME is another regular expression that defines the legal
196       forms for package names.
197

IMPLEMENTATION DETAILS

199   Equivalence between Decimal and Dotted-Decimal Versions
200       When Perl 5.6.0 was released, the decision was made to provide a
201       transformation between the old-style decimal versions and new-style
202       dotted-decimal versions:
203
204         5.6.0    == 5.006000
205         5.005_04 == 5.5.40
206
207       The floating point number is taken and split first on the single
208       decimal place, then each group of three digits to the right of the
209       decimal makes up the next digit, and so on until the number of
210       significant digits is exhausted, plus enough trailing zeros to reach
211       the next multiple of three.
212
213       This was the method that version.pm adopted as well.  Some examples may
214       be helpful:
215
216                                   equivalent
217         decimal    zero-padded    dotted-decimal
218         -------    -----------    --------------
219         1.2        1.200          v1.200.0
220         1.02       1.020          v1.20.0
221         1.002      1.002          v1.2.0
222         1.0023     1.002300       v1.2.300
223         1.00203    1.002030       v1.2.30
224         1.002003   1.002003       v1.2.3
225
226   Quoting Rules
227       Because of the nature of the Perl parsing and tokenizing routines,
228       certain initialization values must be quoted in order to correctly
229       parse as the intended version, especially when using the "declare" or
230       "qv()" methods.  While you do not have to quote decimal numbers when
231       creating version objects, it is always safe to quote all initial values
232       when using version.pm methods, as this will ensure that what you type
233       is what is used.
234
235       Additionally, if you quote your initializer, then the quoted value that
236       goes in will be exactly what comes out when your $VERSION is printed
237       (stringified).  If you do not quote your value, Perl's normal numeric
238       handling comes into play and you may not get back what you were
239       expecting.
240
241       If you use a mathematic formula that resolves to a floating point
242       number, you are dependent on Perl's conversion routines to yield the
243       version you expect.  You are pretty safe by dividing by a power of 10,
244       for example, but other operations are not likely to be what you intend.
245       For example:
246
247         $VERSION = version->new((qw$Revision: 1.4)[1]/10);
248         print $VERSION;          # yields 0.14
249         $V2 = version->new(100/9); # Integer overflow in decimal number
250         print $V2;               # yields something like 11.111.111.100
251
252       Perl 5.8.1 and beyond are able to automatically quote v-strings but
253       that is not possible in earlier versions of Perl.  In other words:
254
255         $version = version->new("v2.5.4");  # legal in all versions of Perl
256         $newvers = version->new(v2.5.4);    # legal only in Perl >= 5.8.1
257
258   What about v-strings?
259       There are two ways to enter v-strings: a bare number with two or more
260       decimal points, or a bare number with one or more decimal points and a
261       leading 'v' character (also bare).  For example:
262
263         $vs1 = 1.2.3; # encoded as \1\2\3
264         $vs2 = v1.2;  # encoded as \1\2
265
266       However, the use of bare v-strings to initialize version objects is
267       strongly discouraged in all circumstances.  Also, bare v-strings are
268       not completely supported in any version of Perl prior to 5.8.1.
269
270       If you insist on using bare v-strings with Perl > 5.6.0, be aware of
271       the following limitations:
272
273       1) For Perl releases 5.6.0 through 5.8.0, the v-string code merely
274       guesses, based on some characteristics of v-strings.  You must use a
275       three part version, e.g. 1.2.3 or v1.2.3 in order for this heuristic to
276       be successful.
277
278       2) For Perl releases 5.8.1 and later, v-strings have changed in the
279       Perl core to be magical, which means that the version.pm code can
280       automatically determine whether the v-string encoding was used.
281
282       3) In all cases, a version created using v-strings will have a
283       stringified form that has a leading 'v' character, for the simple
284       reason that sometimes it is impossible to tell whether one was present
285       initially.
286
287   Version Object Internals
288       version.pm provides an overloaded version object that is designed to
289       both encapsulate the author's intended $VERSION assignment as well as
290       make it completely natural to use those objects as if they were numbers
291       (e.g. for comparisons).  To do this, a version object contains both the
292       original representation as typed by the author, as well as a parsed
293       representation to ease comparisons.  Version objects employ overload
294       methods to simplify code that needs to compare, print, etc the objects.
295
296       The internal structure of version objects is a blessed hash with
297       several components:
298
299           bless( {
300             'original' => 'v1.2.3_4',
301             'alpha' => 1,
302             'qv' => 1,
303             'version' => [
304               1,
305               2,
306               3,
307               4
308             ]
309           }, 'version' );
310
311       original
312           A faithful representation of the value used to initialize this
313           version object.  The only time this will not be precisely the same
314           characters that exist in the source file is if a short dotted-
315           decimal version like v1.2 was used (in which case it will contain
316           'v1.2').  This form is STRONGLY discouraged, in that it will
317           confuse you and your users.
318
319       qv  A boolean that denotes whether this is a decimal or dotted-decimal
320           version.  See "is_qv()" in version.
321
322       alpha
323           A boolean that denotes whether this is an alpha version.  NOTE:
324           that the underscore can only appear in the last position.  See
325           "is_alpha()" in version.
326
327       version
328           An array of non-negative integers that is used for comparison
329           purposes with other version objects.
330
331   Replacement UNIVERSAL::VERSION
332       In addition to the version objects, this modules also replaces the core
333       UNIVERSAL::VERSION function with one that uses version objects for its
334       comparisons.  The return from this operator is always the stringified
335       form as a simple scalar (i.e. not an object), but the warning message
336       generated includes either the stringified form or the normal form,
337       depending on how it was called.
338
339       For example:
340
341         package Foo;
342         $VERSION = 1.2;
343
344         package Bar;
345         $VERSION = "v1.3.5"; # works with all Perl's (since it is quoted)
346
347         package main;
348         use version;
349
350         print $Foo::VERSION; # prints 1.2
351
352         print $Bar::VERSION; # prints 1.003005
353
354         eval "use foo 10";
355         print $@; # prints "foo version 10 required..."
356         eval "use foo 1.3.5; # work in Perl 5.6.1 or better
357         print $@; # prints "foo version 1.3.5 required..."
358
359         eval "use bar 1.3.6";
360         print $@; # prints "bar version 1.3.6 required..."
361         eval "use bar 1.004"; # note Decimal version
362         print $@; # prints "bar version 1.004 required..."
363
364       IMPORTANT NOTE: This may mean that code which searches for a specific
365       string (to determine whether a given module is available) may need to
366       be changed.  It is always better to use the built-in comparison
367       implicit in "use" or "require", rather than manually poking at
368       "class->VERSION" and then doing a comparison yourself.
369
370       The replacement UNIVERSAL::VERSION, when used as a function, like this:
371
372         print $module->VERSION;
373
374       will also exclusively return the stringified form.  See
375       "Stringification" for more details.
376

USAGE DETAILS

378   Using modules that use version.pm
379       As much as possible, the version.pm module remains compatible with all
380       current code.  However, if your module is using a module that has
381       defined $VERSION using the version class, there are a couple of things
382       to be aware of.  For purposes of discussion, we will assume that we
383       have the following module installed:
384
385         package Example;
386         use version;  $VERSION = qv('1.2.2');
387         ...module code here...
388         1;
389
390       Decimal versions always work
391           Code of the form:
392
393             use Example 1.002003;
394
395           will always work correctly.  The "use" will perform an automatic
396           $VERSION comparison using the floating point number given as the
397           first term after the module name (e.g. above 1.002.003).  In this
398           case, the installed module is too old for the requested line, so
399           you would see an error like:
400
401             Example version 1.002003 (v1.2.3) required--this is only version 1.002002 (v1.2.2)...
402
403       Dotted-Decimal version work sometimes
404           With Perl >= 5.6.2, you can also use a line like this:
405
406             use Example 1.2.3;
407
408           and it will again work (i.e. give the error message as above), even
409           with releases of Perl which do not normally support v-strings (see
410           "What about v-strings?" above).  This has to do with that fact that
411           "use" only checks to see if the second term looks like a number and
412           passes that to the replacement UNIVERSAL::VERSION.  This is not
413           true in Perl 5.005_04, however, so you are strongly encouraged to
414           always use a Decimal version in your code, even for those versions
415           of Perl which support the Dotted-Decimal version.
416
417   Object Methods
418       new()
419           Like many OO interfaces, the new() method is used to initialize
420           version objects.  If two arguments are passed to "new()", the
421           second one will be used as if it were prefixed with "v".  This is
422           to support historical use of the "qw" operator with the CVS
423           variable $Revision, which is automatically incremented by CVS every
424           time the file is committed to the repository.
425
426           In order to facilitate this feature, the following code can be
427           employed:
428
429             $VERSION = version->new(qw$Revision: 2.7 $);
430
431           and the version object will be created as if the following code
432           were used:
433
434             $VERSION = version->new("v2.7");
435
436           In other words, the version will be automatically parsed out of the
437           string, and it will be quoted to preserve the meaning CVS normally
438           carries for versions.  The CVS $Revision$ increments differently
439           from Decimal versions (i.e. 1.10 follows 1.9), so it must be
440           handled as if it were a Dotted-Decimal Version.
441
442           A new version object can be created as a copy of an existing
443           version object, either as a class method:
444
445             $v1 = version->new(12.3);
446             $v2 = version->new($v1);
447
448           or as an object method:
449
450             $v1 = version->new(12.3);
451             $v2 = $v1->new(12.3);
452
453           and in each case, $v1 and $v2 will be identical.  NOTE: if you
454           create a new object using an existing object like this:
455
456             $v2 = $v1->new();
457
458           the new object will not be a clone of the existing object.  In the
459           example case, $v2 will be an empty object of the same type as $v1.
460
461       qv()
462           An alternate way to create a new version object is through the
463           exported qv() sub.  This is not strictly like other q? operators
464           (like qq, qw), in that the only delimiters supported are
465           parentheses (or spaces).  It is the best way to initialize a short
466           version without triggering the floating point interpretation.  For
467           example:
468
469             $v1 = qv(1.2);         # v1.2.0
470             $v2 = qv("1.2");       # also v1.2.0
471
472           As you can see, either a bare number or a quoted string can usually
473           be used interchangeably, except in the case of a trailing zero,
474           which must be quoted to be converted properly.  For this reason, it
475           is strongly recommended that all initializers to qv() be quoted
476           strings instead of bare numbers.
477
478           To prevent the "qv()" function from being exported to the caller's
479           namespace, either use version with a null parameter:
480
481             use version ();
482
483           or just require version, like this:
484
485             require version;
486
487           Both methods will prevent the import() method from firing and
488           exporting the "qv()" sub.
489
490       For the subsequent examples, the following three objects will be used:
491
492         $ver   = version->new("1.2.3.4"); # see "Quoting Rules"
493         $alpha = version->new("1.2.3_4"); # see "Alpha Versions"
494         $nver  = version->new(1.002);     # see "Decimal Versions"
495
496       Normal Form
497           For any version object which is initialized with multiple decimal
498           places (either quoted or if possible v-string), or initialized
499           using the qv() operator, the stringified representation is returned
500           in a normalized or reduced form (no extraneous zeros), and with a
501           leading 'v':
502
503             print $ver->normal;         # prints as v1.2.3.4
504             print $ver->stringify;      # ditto
505             print $ver;                 # ditto
506             print $nver->normal;        # prints as v1.2.0
507             print $nver->stringify;     # prints as 1.002,
508                                         # see "Stringification"
509
510           In order to preserve the meaning of the processed version, the
511           normalized representation will always contain at least three sub
512           terms.  In other words, the following is guaranteed to always be
513           true:
514
515             my $newver = version->new($ver->stringify);
516             if ($newver eq $ver ) # always true
517               {...}
518
519       Numification
520           Although all mathematical operations on version objects are
521           forbidden by default, it is possible to retrieve a number which
522           corresponds to the version object through the use of the
523           $obj->numify method.  For formatting purposes, when displaying a
524           number which corresponds a version object, all sub versions are
525           assumed to have three decimal places.  So for example:
526
527             print $ver->numify;         # prints 1.002003004
528             print $nver->numify;        # prints 1.002
529
530           Unlike the stringification operator, there is never any need to
531           append trailing zeros to preserve the correct version value.
532
533       Stringification
534           The default stringification for version objects returns exactly the
535           same string as was used to create it, whether you used "new()" or
536           "qv()", with one exception.  The sole exception is if the object
537           was created using "qv()" and the initializer did not have two
538           decimal places or a leading 'v' (both optional), then the
539           stringified form will have a leading 'v' prepended, in order to
540           support round-trip processing.
541
542           For example:
543
544             Initialized as          Stringifies to
545             ==============          ==============
546             version->new("1.2")       1.2
547             version->new("v1.2")     v1.2
548             qv("1.2.3")               1.2.3
549             qv("v1.3.5")             v1.3.5
550             qv("1.2")                v1.2   ### exceptional case
551
552           See also UNIVERSAL::VERSION, as this also returns the stringified
553           form when used as a class method.
554
555           IMPORTANT NOTE: There is one exceptional cases shown in the above
556           table where the "initializer" is not stringwise equivalent to the
557           stringified representation.  If you use the "qv"() operator on a
558           version without a leading 'v' and with only a single decimal place,
559           the stringified output will have a leading 'v', to preserve the
560           sense.  See the "qv()" operator for more details.
561
562           IMPORTANT NOTE 2: Attempting to bypass the normal stringification
563           rules by manually applying numify() and normal()  will sometimes
564           yield surprising results:
565
566             print version->new(version->new("v1.0")->numify)->normal; # v1.0.0
567
568           The reason for this is that the numify() operator will turn "v1.0"
569           into the equivalent string "1.000000".  Forcing the outer version
570           object to normal() form will display the mathematically equivalent
571           "v1.0.0".
572
573           As the example in "new()" shows, you can always create a copy of an
574           existing version object with the same value by the very compact:
575
576             $v2 = $v1->new($v1);
577
578           and be assured that both $v1 and $v2 will be completely equivalent,
579           down to the same internal representation as well as
580           stringification.
581
582       Comparison operators
583           Both "cmp" and "<=>" operators perform the same comparison between
584           terms (upgrading to a version object automatically).  Perl
585           automatically generates all of the other comparison operators based
586           on those two.  In addition to the obvious equalities listed below,
587           appending a single trailing 0 term does not change the value of a
588           version for comparison purposes.  In other words "v1.2" and "1.2.0"
589           will compare as identical.
590
591           For example, the following relations hold:
592
593             As Number        As String           Truth Value
594             -------------    ----------------    -----------
595             $ver >  1.0      $ver gt "1.0"       true
596             $ver <  2.5      $ver lt             true
597             $ver != 1.3      $ver ne "1.3"       true
598             $ver == 1.2      $ver eq "1.2"       false
599             $ver == 1.2.3.4  $ver eq "1.2.3.4"   see discussion below
600
601           It is probably best to chose either the Decimal notation or the
602           string notation and stick with it, to reduce confusion.  Perl6
603           version objects may only support Decimal comparisons.  See also
604           "Quoting Rules".
605
606           WARNING: Comparing version with unequal numbers of decimal points
607           (whether explicitly or implicitly initialized), may yield
608           unexpected results at first glance.  For example, the following
609           inequalities hold:
610
611             version->new(0.96)     > version->new(0.95); # 0.960.0 > 0.950.0
612             version->new("0.96.1") < version->new(0.95); # 0.096.1 < 0.950.0
613
614           For this reason, it is best to use either exclusively "Decimal
615           Versions" or "Dotted-Decimal Versions" with multiple decimal
616           points.
617
618       Logical Operators
619           If you need to test whether a version object has been initialized,
620           you can simply test it directly:
621
622             $vobj = version->new($something);
623             if ( $vobj )   # true only if $something was non-blank
624
625           You can also test whether a version object is an alpha version, for
626           example to prevent the use of some feature not present in the main
627           release:
628
629             $vobj = version->new("1.2_3"); # MUST QUOTE
630             ...later...
631             if ( $vobj->is_alpha )       # True
632

AUTHOR

634       John Peacock <jpeacock@cpan.org>
635

SEE ALSO

637       perl.
638
639
640
641perl v5.32.0                      2020-09-23             version::Internals(3)
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