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1 | =head1 NAME |
2 | ||
3 | version - Perl extension for Version Objects | |
4 | ||
5 | =head1 SYNOPSIS | |
6 | ||
7 | use version; | |
8 | $version = version->new("12.2.1"); # must be quoted for Perl < 5.8.1 | |
43eaf59d | 9 | print $version; # v12.2.1 |
cb5772bb | 10 | print $version->numify; # 12.002001 |
43eaf59d | 11 | if ( $version gt "12.2" ) # true |
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12 | |
13 | $alphaver = version->new("1.02_03"); # must be quoted! | |
43eaf59d | 14 | print $alphaver; # 1.02_0300 |
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15 | print $alphaver->is_alpha(); # true |
16 | ||
43eaf59d | 17 | $ver = qv("1.2.0"); # v1.2.0 |
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18 | |
19 | $perlver = version->new(5.005_03); # must not be quoted! | |
20 | print $perlver; # 5.005030 | |
21 | ||
22 | =head1 DESCRIPTION | |
23 | ||
24 | Overloaded version objects for all versions of Perl. This module | |
25 | implements all of the features of version objects which will be part | |
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26 | of Perl 5.10.0. |
27 | ||
28 | =head2 BEST PRACTICES | |
29 | ||
30 | If you intend for your module to be used by different releases of Perl, | |
31 | and/or for your $VERSION scalar to mean what you think it means, there | |
32 | are a few simple rules to follow: | |
33 | ||
34 | =over 4 | |
35 | ||
36 | =item * Be consistent | |
37 | ||
38 | Whichever of the two types of version objects that you choose to employ, | |
39 | you should stick to either L<Numeric Versions> or L<Extended Versions> | |
40 | and not mix them together. While this is I<possible>, it is very | |
41 | confusing to the average user. | |
42 | ||
43 | If you intend to use L<Extended Versions>, you are strongly encouraged | |
44 | to use the L<qv()> operator with a quoted term, e.g.: | |
45 | ||
46 | use version; our $VERSION = qv("1.2.3"); | |
47 | ||
48 | on a single line as above. | |
49 | ||
50 | At the very least, decide on which of the several ways to initialize | |
51 | your version objects you prefer and stick with it. It is also best to | |
52 | be explicit about what value you intend to assign your version object | |
53 | and to not rely on hidden behavior of the parser. | |
54 | ||
55 | =item * Be careful | |
56 | ||
57 | If you are using Module::Build or ExtUtils::MakeMaker, so that you can | |
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58 | release your module to CPAN, you have to recognize that neither of those |
59 | programs completely handles version objects natively (yet). If you use | |
60 | version objects with Module::Build, you should add an explicit dependency | |
61 | to the release of version.pm in your Build.PL: | |
62 | ||
63 | my $builder = Module::Build->new( | |
64 | ... | |
65 | requires => { | |
66 | ... , | |
67 | 'version' => 0.50, | |
68 | ..., | |
69 | }, | |
70 | ... | |
71 | ); | |
72 | ||
73 | and it should Just Work(TM). Module::Build will [hopefully soon] | |
74 | include full support for version objects; there are no current plans | |
75 | to patch ExtUtils::MakeMaker to support version objects. | |
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76 | |
77 | =head2 What IS a version | |
78 | ||
79 | For the purposes of this module, a version "number" is a sequence of | |
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80 | positive integer values separated by one or more decimal points and |
81 | optionally a single underscore. This corresponds to what Perl itself | |
82 | uses for a version, as well as extending the "version as number" that | |
83 | is discussed in the various editions of the Camel book. | |
cb5772bb | 84 | |
43eaf59d | 85 | There are actually two distinct kinds of version objects: |
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86 | |
87 | =over 4 | |
88 | ||
89 | =item * Numeric Versions | |
90 | ||
91 | Any initial parameter which "looks like a number", see L<Numeric | |
43eaf59d | 92 | Versions>. This also covers versions with a single decimal point and |
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93 | a single embedded underscore, see L<Numeric Alpha Versions>, even though |
94 | these must be quoted to preserve the underscore formatting. | |
95 | ||
7de739db | 96 | =item * Extended Versions |
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97 | |
98 | Any initial parameter which contains more than one decimal point | |
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99 | and an optional embedded underscore, see L<Extended Versions>. This |
100 | is what is commonly used in most open source software as the "external" | |
101 | version (the one used as part of the tag or tarfile name). The use | |
102 | of the exported L<qv()> function also produces this kind of version | |
103 | object. | |
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104 | |
105 | =back | |
106 | ||
107 | Both of these methods will produce similar version objects, in that | |
108 | the default stringification will yield the version L<Normal Form> only | |
109 | if required: | |
110 | ||
111 | $v = version->new(1.002); # 1.002, but compares like 1.2.0 | |
112 | $v = version->new(1.002003); # 1.002003 | |
113 | $v2 = version->new( "1.2.3"); # v1.2.3 | |
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114 | |
115 | In specific, version numbers initialized as L<Numeric Versions> will | |
7de739db | 116 | stringify in Numeric form. Version numbers initialized as L<Extended Versions> |
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117 | will be stringified as L<Normal Form>. |
118 | ||
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119 | =head2 Numeric Versions |
120 | ||
121 | These correspond to historical versions of Perl itself prior to 5.6.0, | |
122 | as well as all other modules which follow the Camel rules for the | |
123 | $VERSION scalar. A numeric version is initialized with what looks like | |
124 | a floating point number. Leading zeros B<are> significant and trailing | |
125 | zeros are implied so that a minimum of three places is maintained | |
126 | between subversions. What this means is that any subversion (digits | |
127 | to the right of the decimal place) that contains less than three digits | |
128 | will have trailing zeros added to make up the difference, but only for | |
129 | purposes of comparison with other version objects. For example: | |
130 | ||
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131 | # Prints Equivalent to |
132 | $v = version->new( 1.2); # 1.200 v1.200.0 | |
133 | $v = version->new( 1.02); # 1.020 v1.20.0 | |
134 | $v = version->new( 1.002); # 1.002 v1.2.0 | |
135 | $v = version->new( 1.0023); # 1.002300 v1.2.300 | |
136 | $v = version->new( 1.00203); # 1.002030 v1.2.30 | |
137 | $v = version->new( 1.002003); # 1.002003 v1.2.3 | |
cb5772bb | 138 | |
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139 | All of the preceding examples are true whether or not the input value is |
140 | quoted. The important feature is that the input value contains only a | |
141 | single decimal. See also L<Alpha Versions> for how to handle | |
cb5772bb | 142 | |
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143 | IMPORTANT NOTE: As shown above, if your numeric version contains more |
144 | than 3 significant digits after the decimal place, it will be split on | |
145 | each multiple of 3, so 1.0003 is equivalent to v1.0.300, due to the need | |
146 | to remain compatible with Perl's own 5.005_03 == 5.5.30 interpretation. | |
147 | Any trailing zeros are ignored for mathematical comparison purposes. | |
cb5772bb | 148 | |
7de739db | 149 | =head2 Extended Versions |
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150 | |
151 | These are the newest form of versions, and correspond to Perl's own | |
152 | version style beginning with 5.6.0. Starting with Perl 5.10.0, | |
153 | and most likely Perl 6, this is likely to be the preferred form. This | |
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154 | method normally requires that the input parameter be quoted, although |
155 | Perl's after 5.8.1 can use v-strings as a special form of quoting, but | |
156 | this is highly discouraged. | |
cb5772bb | 157 | |
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158 | Unlike L<Numeric Versions>, Extended Versions have more than |
159 | a single decimal point, e.g.: | |
cb5772bb | 160 | |
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161 | # Prints |
162 | $v = version->new( "v1.200"); # v1.200.0 | |
163 | $v = version->new("v1.20.0"); # v1.20.0 | |
164 | $v = qv("v1.2.3); # v1.2.3 | |
165 | $v = qv("1.2.3"); # v1.2.3 | |
166 | $v = qv("1.20"); # v1.20.0 | |
cb5772bb | 167 | |
7de739db | 168 | In general, Extended Versions permit the greatest amount of freedom |
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169 | to specify a version, whereas Numeric Versions enforce a certain |
170 | uniformity. See also L<New Operator> for an additional method of | |
171 | initializing version objects. | |
172 | ||
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173 | Just like L<Numeric Versions>, Extended Versions can be used as |
174 | L<Alpha Versions>. | |
175 | ||
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176 | =head2 Numeric Alpha Versions |
177 | ||
178 | The one time that a numeric version must be quoted is when a alpha form is | |
43eaf59d | 179 | used with an otherwise numeric version (i.e. a single decimal point). This |
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180 | is commonly used for CPAN releases, where CPAN or CPANPLUS will ignore alpha |
181 | versions for automatic updating purposes. Since some developers have used | |
182 | only two significant decimal places for their non-alpha releases, the | |
183 | version object will automatically take that into account if the initializer | |
184 | is quoted. For example Module::Example was released to CPAN with the | |
185 | following sequence of $VERSION's: | |
186 | ||
187 | # $VERSION Stringified | |
188 | 0.01 0.010 | |
189 | 0.02 0.020 | |
190 | 0.02_01 0.02_0100 | |
191 | 0.02_02 0.02_0200 | |
192 | 0.03 0.030 | |
193 | etc. | |
194 | ||
195 | As you can see, the version object created from the values in the first | |
196 | column may contain a trailing 0, but will otherwise be both mathematically | |
197 | equivalent and sorts alpha-numerically as would be expected. | |
198 | ||
199 | =head2 Object Methods | |
200 | ||
201 | Overloading has been used with version objects to provide a natural | |
202 | interface for their use. All mathematical operations are forbidden, | |
203 | since they don't make any sense for base version objects. | |
204 | ||
205 | =over 4 | |
206 | ||
207 | =item * New Operator | |
208 | ||
209 | Like all OO interfaces, the new() operator is used to initialize | |
210 | version objects. One way to increment versions when programming is to | |
211 | use the CVS variable $Revision, which is automatically incremented by | |
212 | CVS every time the file is committed to the repository. | |
213 | ||
214 | In order to facilitate this feature, the following | |
215 | code can be employed: | |
216 | ||
217 | $VERSION = version->new(qw$Revision: 2.7 $); | |
218 | ||
219 | and the version object will be created as if the following code | |
220 | were used: | |
221 | ||
222 | $VERSION = version->new("v2.7"); | |
223 | ||
224 | In other words, the version will be automatically parsed out of the | |
225 | string, and it will be quoted to preserve the meaning CVS normally | |
226 | carries for versions. The CVS $Revision$ increments differently from | |
227 | numeric versions (i.e. 1.10 follows 1.9), so it must be handled as if | |
7de739db | 228 | it were a L<Extended Version>. |
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229 | |
230 | A new version object can be created as a copy of an existing version | |
231 | object, either as a class method: | |
232 | ||
233 | $v1 = version->new(12.3); | |
234 | $v2 = version->new($v1); | |
235 | ||
236 | or as an object method: | |
237 | ||
238 | $v1 = version->new(12.3); | |
239 | $v2 = $v1->new(); | |
240 | ||
241 | and in each case, $v1 and $v2 will be identical. | |
242 | ||
243 | =back | |
244 | ||
245 | =over 4 | |
246 | ||
247 | =item * qv() | |
248 | ||
249 | An alternate way to create a new version object is through the exported | |
250 | qv() sub. This is not strictly like other q? operators (like qq, qw), | |
251 | in that the only delimiters supported are parentheses (or spaces). It is | |
252 | the best way to initialize a short version without triggering the floating | |
253 | point interpretation. For example: | |
254 | ||
255 | $v1 = qv(1.2); # 1.2.0 | |
256 | $v2 = qv("1.2"); # also 1.2.0 | |
257 | ||
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258 | As you can see, either a bare number or a quoted string can usually |
259 | be used interchangably, except in the case of a trailing zero, which | |
260 | must be quoted to be converted properly. For this reason, it is strongly | |
261 | recommended that all initializers to qv() be quoted strings instead of | |
262 | bare numbers. | |
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263 | |
264 | =back | |
265 | ||
266 | For the subsequent examples, the following three objects will be used: | |
267 | ||
268 | $ver = version->new("1.2.3.4"); # see "Quoting" below | |
269 | $alpha = version->new("1.2.3_4"); # see "Alpha versions" below | |
43eaf59d | 270 | $nver = version->new(1.002); # see "Numeric Versions" above |
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271 | |
272 | =over 4 | |
273 | ||
274 | =item * Normal Form | |
275 | ||
276 | For any version object which is initialized with multiple decimal | |
277 | places (either quoted or if possible v-string), or initialized using | |
278 | the L<qv()> operator, the stringified representation is returned in | |
279 | a normalized or reduced form (no extraneous zeros), and with a leading 'v': | |
280 | ||
43eaf59d | 281 | print $ver->normal; # prints as v1.2.3.4 |
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282 | print $ver->stringify; # ditto |
283 | print $ver; # ditto | |
284 | print $nver->normal; # prints as v1.2.0 | |
285 | print $nver->stringify; # prints as 1.002, see "Stringification" | |
286 | ||
287 | In order to preserve the meaning of the processed version, the | |
288 | normalized representation will always contain at least three sub terms. | |
289 | In other words, the following is guaranteed to always be true: | |
290 | ||
291 | my $newver = version->new($ver->stringify); | |
292 | if ($newver eq $ver ) # always true | |
293 | {...} | |
294 | ||
295 | =back | |
296 | ||
297 | =over 4 | |
298 | ||
299 | =item * Numification | |
300 | ||
301 | Although all mathematical operations on version objects are forbidden | |
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302 | by default, it is possible to retrieve a number which corresponds |
303 | to the version object through the use of the $obj->numify | |
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304 | method. For formatting purposes, when displaying a number which |
305 | corresponds a version object, all sub versions are assumed to have | |
306 | three decimal places. So for example: | |
307 | ||
43eaf59d | 308 | print $ver->numify; # prints 1.002003004 |
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309 | print $nver->numify; # prints 1.002 |
310 | ||
311 | Unlike the stringification operator, there is never any need to append | |
312 | trailing zeros to preserve the correct version value. | |
313 | ||
314 | =back | |
315 | ||
316 | =over 4 | |
317 | ||
318 | =item * Stringification | |
319 | ||
320 | In order to mirror as much as possible the existing behavior of ordinary | |
321 | $VERSION scalars, the stringification operation will display differently, | |
322 | depending on whether the version was initialized as a L<Numeric Version> | |
7de739db | 323 | or L<Extended Version>. |
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324 | |
325 | What this means in practice is that if the normal CPAN and Camel rules are | |
326 | followed ($VERSION is a floating point number with no more than 3 decimal | |
43eaf59d | 327 | points), the stringified output will be exactly the same as the numified |
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328 | output. There will be no visible difference, although the internal |
329 | representation will be different, and the L<Comparison operators> will | |
330 | function using the internal coding. | |
331 | ||
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332 | If a version object is initialized using a L<Extended Version> form, then |
333 | the stringified form will be the L<Normal Form>. The $obj->normal | |
334 | operation can always be used to produce the L<Normal Form>, even if the | |
335 | version was originally a L<Numeric Version>. | |
cb5772bb | 336 | |
43eaf59d | 337 | print $ver->stringify; # prints v1.2.3.4 |
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338 | print $nver->stringify; # prints 1.002 |
339 | ||
340 | =back | |
341 | ||
342 | =over 4 | |
343 | ||
344 | =item * Comparison operators | |
345 | ||
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346 | Both C<cmp> and C<E<lt>=E<gt>> operators perform the same comparison between |
347 | terms (upgrading to a version object automatically). Perl automatically | |
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348 | generates all of the other comparison operators based on those two. |
349 | In addition to the obvious equalities listed below, appending a single | |
350 | trailing 0 term does not change the value of a version for comparison | |
351 | purposes. In other words "v1.2" and "1.2.0" will compare as identical. | |
352 | ||
353 | For example, the following relations hold: | |
354 | ||
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355 | As Number As String Truth Value |
356 | ------------- ---------------- ----------- | |
357 | $ver > 1.0 $ver gt "1.0" true | |
358 | $ver < 2.5 $ver lt true | |
359 | $ver != 1.3 $ver ne "1.3" true | |
360 | $ver == 1.2 $ver eq "1.2" false | |
361 | $ver == 1.2.3.4 $ver eq "1.2.3.4" see discussion below | |
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362 | |
363 | It is probably best to chose either the numeric notation or the string | |
364 | notation and stick with it, to reduce confusion. Perl6 version objects | |
43eaf59d | 365 | B<may> only support numeric comparisons. See also L<Quoting>. |
cb5772bb | 366 | |
43eaf59d | 367 | WARNING: Comparing version with unequal numbers of decimal points (whether |
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368 | explicitly or implicitly initialized), may yield unexpected results at |
369 | first glance. For example, the following inequalities hold: | |
370 | ||
371 | version->new(0.96) > version->new(0.95); # 0.960.0 > 0.950.0 | |
372 | version->new("0.96.1") < version->new(0.95); # 0.096.1 < 0.950.0 | |
373 | ||
374 | For this reason, it is best to use either exclusively L<Numeric Versions> or | |
43eaf59d | 375 | L<Extended Versions> with multiple decimal points. |
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376 | |
377 | =back | |
378 | ||
379 | =over 4 | |
380 | ||
381 | =item * Logical Operators | |
382 | ||
383 | If you need to test whether a version object | |
384 | has been initialized, you can simply test it directly: | |
385 | ||
386 | $vobj = version->new($something); | |
387 | if ( $vobj ) # true only if $something was non-blank | |
388 | ||
389 | You can also test whether a version object is an L<Alpha version>, for | |
390 | example to prevent the use of some feature not present in the main | |
391 | release: | |
392 | ||
393 | $vobj = version->new("1.2_3"); # MUST QUOTE | |
394 | ...later... | |
395 | if ( $vobj->is_alpha ) # True | |
396 | ||
397 | =back | |
398 | ||
399 | =head2 Quoting | |
400 | ||
401 | Because of the nature of the Perl parsing and tokenizing routines, | |
402 | certain initialization values B<must> be quoted in order to correctly | |
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403 | parse as the intended version, especially when using the L<qv()> operator. |
404 | In all cases, a floating point number passed to version->new() will be | |
405 | identically converted whether or not the value itself is quoted. This is | |
406 | not true for L<qv()>, however, when trailing zeros would be stripped on | |
407 | an unquoted input, which would result in a very different version object. | |
408 | ||
409 | In addition, in order to be compatible with earlier Perl version styles, | |
410 | any use of versions of the form 5.006001 will be translated as v5.6.1. | |
411 | In other words, a version with a single decimal point will be parsed as | |
412 | implicitly having three digits between subversions, but only for internal | |
413 | comparison purposes. | |
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414 | |
415 | The complicating factor is that in bare numbers (i.e. unquoted), the | |
416 | underscore is a legal numeric character and is automatically stripped | |
417 | by the Perl tokenizer before the version code is called. However, if | |
418 | a number containing one or more decimals and an underscore is quoted, i.e. | |
419 | not bare, that is considered a L<Alpha Version> and the underscore is | |
420 | significant. | |
421 | ||
422 | If you use a mathematic formula that resolves to a floating point number, | |
423 | you are dependent on Perl's conversion routines to yield the version you | |
424 | expect. You are pretty safe by dividing by a power of 10, for example, | |
425 | but other operations are not likely to be what you intend. For example: | |
426 | ||
427 | $VERSION = version->new((qw$Revision: 1.4)[1]/10); | |
428 | print $VERSION; # yields 0.14 | |
429 | $V2 = version->new(100/9); # Integer overflow in decimal number | |
430 | print $V2; # yields something like 11.111.111.100 | |
431 | ||
432 | Perl 5.8.1 and beyond will be able to automatically quote v-strings but | |
433 | that is not possible in earlier versions of Perl. In other words: | |
434 | ||
435 | $version = version->new("v2.5.4"); # legal in all versions of Perl | |
436 | $newvers = version->new(v2.5.4); # legal only in Perl >= 5.8.1 | |
437 | ||
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438 | =head2 What about v-strings? |
439 | ||
440 | Beginning with Perl 5.6.0, an alternate method to code arbitrary strings | |
441 | of bytes was introduced, called v-strings. They were intended to be an | |
442 | easy way to enter, for example, Unicode strings (which contain two bytes | |
443 | per character). Some programs have used them to encode printer control | |
444 | characters (e.g. CRLF). They were also intended to be used for $VERSION, | |
445 | but their use as such has been problematic from the start. | |
446 | ||
447 | There are two ways to enter v-strings: a bare number with two or more | |
448 | decimal points, or a bare number with one or more decimal points and a | |
449 | leading 'v' character (also bare). For example: | |
450 | ||
451 | $vs1 = 1.2.3; # encoded as \1\2\3 | |
452 | $vs2 = v1.2; # encoded as \1\2 | |
453 | ||
454 | However, the use of v-strings to initialize version objects with this | |
455 | module is only possible with Perl 5.8.1 or better (which contain special | |
456 | code to enable it). Their use is B<strongly> discouraged in all | |
457 | circumstances (especially the leading 'v' style), since the meaning will | |
458 | change depending on which Perl you are running. It is better to directly | |
459 | use L<"Extended Versions"> to ensure the proper interpretation. | |
460 | ||
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461 | |
462 | =head2 Types of Versions Objects | |
463 | ||
464 | There are two types of Version Objects: | |
465 | ||
466 | =over 4 | |
467 | ||
468 | =item * Ordinary versions | |
469 | ||
470 | These are the versions that normal modules will use. Can contain as | |
471 | many subversions as required. In particular, those using RCS/CVS can | |
472 | use the following: | |
473 | ||
474 | $VERSION = version->new(qw$Revision: 2.7 $); | |
475 | ||
476 | and the current RCS Revision for that file will be inserted | |
477 | automatically. If the file has been moved to a branch, the Revision | |
478 | will have three or more elements; otherwise, it will have only two. | |
479 | This allows you to automatically increment your module version by | |
480 | using the Revision number from the primary file in a distribution, see | |
481 | L<ExtUtils::MakeMaker/"VERSION_FROM">. | |
482 | ||
483 | =item * Alpha Versions | |
484 | ||
485 | For module authors using CPAN, the convention has been to note | |
486 | unstable releases with an underscore in the version string, see | |
487 | L<CPAN>. Alpha releases will test as being newer than the more recent | |
488 | stable release, and less than the next stable release. For example: | |
489 | ||
490 | $alphaver = version->new("12.03_01"); # must be quoted | |
491 | ||
492 | obeys the relationship | |
493 | ||
494 | 12.03 < $alphaver < 12.04 | |
495 | ||
43eaf59d | 496 | Alpha versions with a single decimal point will be treated exactly as if |
cb5772bb | 497 | they were L<Numeric Versions>, for parsing purposes. The stringification for |
43eaf59d | 498 | alpha versions with a single decimal point may seem surprising, since any |
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499 | trailing zeros will visible. For example, the above $alphaver will print as |
500 | ||
501 | 12.03_0100 | |
502 | ||
503 | which is mathematically equivalent and ASCII sorts exactly the same as | |
504 | without the trailing zeros. | |
505 | ||
43eaf59d | 506 | Alpha versions with more than a single decimal point will be treated |
7de739db | 507 | exactly as if they were L<Extended Versions>, and will display without any |
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508 | trailing (or leading) zeros, in the L<Version Normal> form. For example, |
509 | ||
510 | $newver = version->new("12.3.1_1"); | |
511 | print $newver; # v12.3.1_1 | |
512 | ||
513 | =head2 Replacement UNIVERSAL::VERSION | |
514 | ||
515 | In addition to the version objects, this modules also replaces the core | |
516 | UNIVERSAL::VERSION function with one that uses version objects for its | |
517 | comparisons. The return from this operator is always the numified form, | |
518 | and the warning message generated includes both the numified and normal | |
519 | forms (for clarity). | |
520 | ||
521 | For example: | |
522 | ||
523 | package Foo; | |
524 | $VERSION = 1.2; | |
525 | ||
526 | package Bar; | |
527 | $VERSION = "1.3.5"; # works with all Perl's (since it is quoted) | |
528 | ||
529 | package main; | |
530 | use version; | |
531 | ||
532 | print $Foo::VERSION; # prints 1.2 | |
533 | ||
534 | print $Bar::VERSION; # prints 1.003005 | |
535 | ||
536 | eval "use CGI 10"; # some far future release | |
537 | print $@; # prints "CGI version 10 (10.0.0) required..." | |
538 | ||
539 | IMPORTANT NOTE: This may mean that code which searches for a specific | |
540 | string (to determine whether a given module is available) may need to be | |
541 | changed. | |
542 | ||
543 | The replacement UNIVERSAL::VERSION, when used as a function, like this: | |
544 | ||
545 | print $module->VERSION; | |
546 | ||
547 | will also exclusively return the numified form. Technically, the | |
548 | $module->VERSION function returns a string (PV) that can be converted to a | |
549 | number following the normal Perl rules, when used in a numeric context. | |
550 | ||
551 | =head1 SUBCLASSING | |
552 | ||
553 | This module is specifically designed and tested to be easily subclassed. | |
554 | In practice, you only need to override the methods you want to change, but | |
555 | you have to take some care when overriding new() (since that is where all | |
556 | of the parsing takes place). For example, this is a perfect acceptable | |
557 | derived class: | |
558 | ||
559 | package myversion; | |
560 | use base version; | |
561 | sub new { | |
562 | my($self,$n)=@_; | |
563 | my $obj; | |
564 | # perform any special input handling here | |
565 | $obj = $self->SUPER::new($n); | |
566 | # and/or add additional hash elements here | |
567 | return $obj; | |
568 | } | |
569 | ||
570 | See also L<version::AlphaBeta> on CPAN for an alternate representation of | |
571 | version strings. | |
572 | ||
7de739db SP |
573 | B<NOTE:> the L<qv> operator is not a class method and will not be inherited |
574 | in the same way as the other methods. L<qv> will always return an object of | |
575 | type L<version> and not an object in the derived class. If you need to | |
576 | have L<qv> return an object in your derived class, add something like this: | |
cb5772bb | 577 | |
7de739db | 578 | *::qv = sub { return bless version::qv(shift), __PACKAGE__ }; |
cb5772bb | 579 | |
7de739db | 580 | as seen in the test file F<t/02derived.t>. |
cb5772bb RGS |
581 | |
582 | =head1 EXPORT | |
583 | ||
7de739db | 584 | qv - Extended Version initialization operator |
cb5772bb RGS |
585 | |
586 | =head1 AUTHOR | |
587 | ||
588 | John Peacock E<lt>jpeacock@cpan.orgE<gt> | |
589 | ||
590 | =head1 SEE ALSO | |
591 | ||
592 | L<perl>. | |
593 | ||
594 | =cut |