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version::Internals(3)  Perl Programmers	Reference Guide	 version::Internals(3)

       version::Internals - Perl extension for Version Objects

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

       For the purposes	of this	module,	a version "number" is a	sequence of
       positive	integer	values separated by one	or more	decimal	points and
       optionally a single underscore.	This corresponds to what Perl itself
       uses for	a version, as well as extending	the "version as	number"	that
       is discussed in the various editions of the Camel book.

       There are actually two distinct kinds of	version	objects:

       Decimal versions
	   Any version which "looks like a number", see	"Decimal Versions".
	   This	also includes versions with a single decimal point and a
	   single embedded underscore, see "Alpha Versions", even though these
	   must	be quoted to preserve the underscore formatting.

       Dotted-Decimal versions
	   Also	referred to as "Dotted-Integer", these contains	more than one
	   decimal point and may have an optional embedded underscore, see
	   Dotted-Decimal Versions.  This is what is commonly used in most
	   open	source software	as the "external" version (the one used	as
	   part	of the tag or tarfile name).  A	leading	'v' character is now
	   required and	will warn if it	missing.

       Both of these methods will produce similar version objects, in that the
       default stringification will yield the version "Normal Form" only if

	 $v  = version->new(1.002);	# 1.002, but compares like 1.2.0
	 $v  = version->new(1.002003);	# 1.002003
	 $v2 = version->new("v1.2.3");	# v1.2.3

       In specific, version numbers initialized	as "Decimal Versions" will
       stringify as they were originally created (i.e. the same	string that
       was passed to "new()".  Version numbers initialized as "Dotted-Decimal
       Versions" will be stringified as	"Normal	Form".

   Decimal Versions
       These correspond	to historical versions of Perl itself prior to 5.6.0,
       as well as all other modules which follow the Camel rules for the
       $VERSION	scalar.	 A Decimal version is initialized with what looks like
       a floating point	number.	 Leading zeros are significant and trailing
       zeros are implied so that a minimum of three places is maintained
       between subversions.  What this means is	that any subversion (digits to
       the right of the	decimal	place) that contains less than three digits
       will have trailing zeros	added to make up the difference, but only for
       purposes	of comparison with other version objects.  For example:

					  # Prints     Equivalent to
	 $v = version->new(	 1.2);	  # 1.2	       v1.200.0
	 $v = version->new(	1.02);	  # 1.02       v1.20.0
	 $v = version->new(    1.002);	  # 1.002      v1.2.0
	 $v = version->new(   1.0023);	  # 1.0023     v1.2.300
	 $v = version->new(  1.00203);	  # 1.00203    v1.2.30
	 $v = version->new( 1.002003);	  # 1.002003   v1.2.3

       All of the preceding examples are true whether or not the input value
       is quoted.  The important feature is that the input value contains only
       a single	decimal.  See also "Alpha Versions".

       IMPORTANT NOTE: As shown	above, if your Decimal version contains	more
       than 3 significant digits after the decimal place, it will be split on
       each multiple of	3, so 1.0003 is	equivalent to v1.0.300,	due to the
       need to remain compatible with Perl's own 5.005_03 == 5.5.30
       interpretation.	Any trailing zeros are ignored for mathematical
       comparison purposes.

   Dotted-Decimal Versions
       These are the newest form of versions, and correspond to	Perl's own
       version style beginning with 5.6.0.  Starting with Perl 5.10.0, and
       most likely Perl	6, this	is likely to be	the preferred form.  This
       method normally requires	that the input parameter be quoted, although
       Perl's after 5.8.1 can use v-strings as a special form of quoting, but
       this is highly discouraged.

       Unlike "Decimal Versions", Dotted-Decimal Versions have more than a
       single decimal point, e.g.:

					  # Prints
	 $v = version->new( "v1.200");	  # v1.200.0
	 $v = version->new("v1.20.0");	  # v1.20.0
	 $v = qv("v1.2.3");		  # v1.2.3
	 $v = qv("1.2.3");		  # v1.2.3
	 $v = qv("1.20");		  # v1.20.0

       In general, Dotted-Decimal Versions permit the greatest amount of
       freedom to specify a version, whereas Decimal Versions enforce a
       certain uniformity.

       Just like "Decimal Versions", Dotted-Decimal Versions can be used as
       "Alpha Versions".

   Alpha Versions
       For module authors using	CPAN, the convention has been to note unstable
       releases	with an	underscore in the version string. (See CPAN.) follows this convention and alpha releases will test as
       being newer than	the more recent	stable release,	and less than the next
       stable release.	Only the last element may be separated by an

	 # Declaring
	 use version 0.77; our $VERSION	= version->declare("v1.2_3");

	 # Parsing
	 $v1 = version->parse("v1.2_3");
	 $v1 = version->parse("1.002_003");

       Note that you must quote	the version when writing an alpha Decimal
       version.	 The stringified form of Decimal versions will always be the
       same string that	was used to initialize the version object.

   Regular Expressions for Version Parsing
       A formalized definition of the legal forms for version strings is
       included	in the "version::regex"	class.	Primitives are included	for
       common elements,	although they are scoped to the	file so	they are
       useful for reference purposes only.  There are two publicly accessible
       scalars that can	be used	in other code (not exported):

	   This	regexp covers all of the legal forms allowed under the current
	   version string parser.  This	is not to say that all of these	forms
	   are recommended, and	some of	them can only be used when quoted.

	   For dotted decimals:


	   The leading 'v' is optional if two or more decimals appear.	If
	   only	a single decimal is included, then the leading 'v' is required
	   to trigger the dotted-decimal parsing.  A leading zero is
	   permitted, though not recommended except when quoted, because of
	   the risk that Perl will treat the number as octal.  A trailing
	   underscore plus one or more digits denotes an alpha or development
	   release (and	must be	quoted to be parsed properly).

	   For decimal versions:


	   an integer portion, an optional decimal point, and optionally one
	   or more digits to the right of the decimal are all required.	 A
	   trailing underscore is permitted and	a leading zero is permitted.
	   Just	like the lax dotted-decimal version, quoting the values	is
	   required for	alpha/development forms	to be parsed correctly.

	   This	regexp covers a	much more limited set of formats and
	   constitutes the best	practices for initializing version objects.
	   Whether you choose to employ	decimal	or dotted-decimal for is a
	   personal preference however.

	       For dotted-decimal versions, a leading 'v' is required, with
	       three or	more sub-versions of no	more than three	digits.	 A
	       leading 0 (zero)	before the first sub-version (in the above
	       example,	'1') is	also prohibited.

	       For decimal versions, an	integer	portion	(no leading 0),	a
	       decimal point, and one or more digits to	the right of the
	       decimal are all required.

       Both of the provided scalars are	already	compiled as regular
       expressions and do not contain either anchors or	implicit groupings, so
       they can	be included in your own	regular	expressions freely.  For
       example,	consider the following code:

	       ($pkg, $ver) =~ /
		       ^[ \t]*
		       use [ \t]+($PKGNAME)
		       (?:[ \t]+($version::STRICT))?
		       [ \t]*;

       This would match	a line of the form:

	       use Foo::Bar::Baz v1.2.3;       # legal only in Perl 5.8.1+

       where $PKGNAME is another regular expression that defines the legal
       forms for package names.

   Equivalence between Decimal and Dotted-Decimal Versions
       When Perl 5.6.0 was released, the decision was made to provide a
       transformation between the old-style decimal versions and new-style
       dotted-decimal versions:

	 5.6.0	  == 5.006000
	 5.005_04 == 5.5.40

       The floating point number is taken and split first on the single
       decimal place, then each	group of three digits to the right of the
       decimal makes up	the next digit,	and so on until	the number of
       significant digits is exhausted,	plus enough trailing zeros to reach
       the next	multiple of three.

       This was	the method that adopted as well.  Some examples may
       be helpful:

	 decimal    zero-padded	   dotted-decimal
	 -------    -----------	   --------------
	 1.2	    1.200	   v1.200.0
	 1.02	    1.020	   v1.20.0
	 1.002	    1.002	   v1.2.0
	 1.0023	    1.002300	   v1.2.300
	 1.00203    1.002030	   v1.2.30
	 1.002003   1.002003	   v1.2.3

   Quoting Rules
       Because of the nature of	the Perl parsing and tokenizing	routines,
       certain initialization values must be quoted in order to	correctly
       parse as	the intended version, especially when using the	"declare" or
       "qv()" methods.	While you do not have to quote decimal numbers when
       creating	version	objects, it is always safe to quote all	initial	values
       when using methods, as this will ensure that what you	type
       is what is used.

       Additionally, if	you quote your initializer, then the quoted value that
       goes in will be exactly what comes out when your	$VERSION is printed
       (stringified).  If you do not quote your	value, Perl's normal numeric
       handling	comes into play	and you	may not	get back what you were

       If you use a mathematic formula that resolves to	a floating point
       number, you are dependent on Perl's conversion routines to yield	the
       version you expect.  You	are pretty safe	by dividing by a power of 10,
       for example, but	other operations are not likely	to be what you intend.
       For example:

	 $VERSION = version->new((qw$Revision: 1.4)[1]/10);
	 print $VERSION;	  # yields 0.14
	 $V2 = version->new(100/9); # Integer overflow in decimal number
	 print $V2;		  # yields something like

       Perl 5.8.1 and beyond are able to automatically quote v-strings but
       that is not possible in earlier versions	of Perl.  In other words:

	 $version = version->new("v2.5.4");  # legal in	all versions of	Perl
	 $newvers = version->new(v2.5.4);    # legal only in Perl >= 5.8.1

   What	about v-strings?
       There are two ways to enter v-strings: a	bare number with two or	more
       decimal points, or a bare number	with one or more decimal points	and a
       leading 'v' character (also bare).  For example:

	 $vs1 =	1.2.3; # encoded as \1\2\3
	 $vs2 =	v1.2;  # encoded as \1\2

       However,	the use	of bare	v-strings to initialize	version	objects	is
       strongly	discouraged in all circumstances.  Also, bare v-strings	are
       not completely supported	in any version of Perl prior to	5.8.1.

       If you insist on	using bare v-strings with Perl > 5.6.0,	be aware of
       the following limitations:

       1) For Perl releases 5.6.0 through 5.8.0, the v-string code merely
       guesses,	based on some characteristics of v-strings.  You must use a
       three part version, e.g.	1.2.3 or v1.2.3	in order for this heuristic to
       be successful.

       2) For Perl releases 5.8.1 and later, v-strings have changed in the
       Perl core to be magical,	which means that the	code can
       automatically determine whether the v-string encoding was used.

       3) In all cases,	a version created using	v-strings will have a
       stringified form	that has a leading 'v' character, for the simple
       reason that sometimes it	is impossible to tell whether one was present

   Version Object Internals provides an overloaded version object	that is	designed to
       both encapsulate	the author's intended $VERSION assignment as well as
       make it completely natural to use those objects as if they were numbers
       (e.g. for comparisons).	To do this, a version object contains both the
       original	representation as typed	by the author, as well as a parsed
       representation to ease comparisons.  Version objects employ overload
       methods to simplify code	that needs to compare, print, etc the objects.

       The internal structure of version objects is a blessed hash with
       several components:

	   bless( {
	     'original'	=> 'v1.2.3_4',
	     'alpha' =>	1,
	     'qv' => 1,
	     'version' => [
	   }, 'version'	);

	   A faithful representation of	the value used to initialize this
	   version object.  The	only time this will not	be precisely the same
	   characters that exist in the	source file is if a short dotted-
	   decimal version like	v1.2 was used (in which	case it	will contain
	   'v1.2').  This form is STRONGLY discouraged,	in that	it will
	   confuse you and your	users.

       qv  A boolean that denotes whether this is a decimal or dotted-decimal
	   version.  See "is_qv()" in version.

	   A boolean that denotes whether this is an alpha version.  NOTE:
	   that	the underscore can only	appear in the last position.  See
	   "is_alpha()"	in version.

	   An array of non-negative integers that is used for comparison
	   purposes with other version objects.

       In addition to the version objects, this	modules	also replaces the core
       UNIVERSAL::VERSION function with	one that uses version objects for its
       comparisons.  The return	from this operator is always the stringified
       form as a simple	scalar (i.e. not an object), but the warning message
       generated includes either the stringified form or the normal form,
       depending on how	it was called.

       For example:

	 package Foo;
	 $VERSION = 1.2;

	 package Bar;
	 $VERSION = "v1.3.5"; #	works with all Perl's (since it	is quoted)

	 package main;
	 use version;

	 print $Foo::VERSION; #	prints 1.2

	 print $Bar::VERSION; #	prints 1.003005

	 eval "use foo 10";
	 print $@; # prints "foo version 10 required..."
	 eval "use foo 1.3.5; #	work in	Perl 5.6.1 or better
	 print $@; # prints "foo version 1.3.5 required..."

	 eval "use bar 1.3.6";
	 print $@; # prints "bar version 1.3.6 required..."
	 eval "use bar 1.004"; # note Decimal version
	 print $@; # prints "bar version 1.004 required..."

       IMPORTANT NOTE: This may	mean that code which searches for a specific
       string (to determine whether a given module is available) may need to
       be changed.  It is always better	to use the built-in comparison
       implicit	in "use" or "require", rather than manually poking at
       "class->VERSION"	and then doing a comparison yourself.

       The replacement UNIVERSAL::VERSION, when	used as	a function, like this:

	 print $module->VERSION;

       will also exclusively return the	stringified form.  See
       "Stringification" for more details.

   Using modules that use
       As much as possible, the module remains compatible with all
       current code.  However, if your module is using a module	that has
       defined $VERSION	using the version class, there are a couple of things
       to be aware of.	For purposes of	discussion, we will assume that	we
       have the	following module installed:

	 package Example;
	 use version;  $VERSION	= qv('1.2.2');
	 ...module code	here...

       Decimal versions	always work
	   Code	of the form:

	     use Example 1.002003;

	   will	always work correctly.	The "use" will perform an automatic
	   $VERSION comparison using the floating point	number given as	the
	   first term after the	module name (e.g. above	1.002.003).  In	this
	   case, the installed module is too old for the requested line, so
	   you would see an error like:

	     Example version 1.002003 (v1.2.3) required--this is only version 1.002002 (v1.2.2)...

       Dotted-Decimal version work sometimes
	   With	Perl >=	5.6.2, you can also use	a line like this:

	     use Example 1.2.3;

	   and it will again work (i.e.	give the error message as above), even
	   with	releases of Perl which do not normally support v-strings (see
	   "What about v-strings?" above).  This has to	do with	that fact that
	   "use" only checks to	see if the second term looks like a number and
	   passes that to the replacement UNIVERSAL::VERSION.  This is not
	   true	in Perl	5.005_04, however, so you are strongly encouraged to
	   always use a	Decimal	version	in your	code, even for those versions
	   of Perl which support the Dotted-Decimal version.

   Object Methods
	   Like	many OO	interfaces, the	new() method is	used to	initialize
	   version objects.  If	two arguments are passed to "new()", the
	   second one will be used as if it were prefixed with "v".  This is
	   to support historical use of	the "qw" operator with the CVS
	   variable $Revision, which is	automatically incremented by CVS every
	   time	the file is committed to the repository.

	   In order to facilitate this feature,	the following code can be

	     $VERSION =	version->new(qw$Revision: 2.7 $);

	   and the version object will be created as if	the following code
	   were	used:

	     $VERSION =	version->new("v2.7");

	   In other words, the version will be automatically parsed out	of the
	   string, and it will be quoted to preserve the meaning CVS normally
	   carries for versions.  The CVS $Revision$ increments	differently
	   from	Decimal	versions (i.e. 1.10 follows 1.9), so it	must be
	   handled as if it were a Dotted-Decimal Version.

	   A new version object	can be created as a copy of an existing
	   version object, either as a class method:

	     $v1 = version->new(12.3);
	     $v2 = version->new($v1);

	   or as an object method:

	     $v1 = version->new(12.3);
	     $v2 = $v1->new(12.3);

	   and in each case, $v1 and $v2 will be identical.  NOTE: if you
	   create a new	object using an	existing object	like this:

	     $v2 = $v1->new();

	   the new object will not be a	clone of the existing object.  In the
	   example case, $v2 will be an	empty object of	the same type as $v1.

	   An alternate	way to create a	new version object is through the
	   exported qv() sub.  This is not strictly like other q? operators
	   (like qq, qw), in that the only delimiters supported	are
	   parentheses (or spaces).  It	is the best way	to initialize a	short
	   version without triggering the floating point interpretation.  For

	     $v1 = qv(1.2);	    # v1.2.0
	     $v2 = qv("1.2");	    # also v1.2.0

	   As you can see, either a bare number	or a quoted string can usually
	   be used interchangeably, except in the case of a trailing zero,
	   which must be quoted	to be converted	properly.  For this reason, it
	   is strongly recommended that	all initializers to qv() be quoted
	   strings instead of bare numbers.

	   To prevent the "qv()" function from being exported to the caller's
	   namespace, either use version with a	null parameter:

	     use version ();

	   or just require version, like this:

	     require version;

	   Both	methods	will prevent the import() method from firing and
	   exporting the "qv()"	sub.

       For the subsequent examples, the	following three	objects	will be	used:

	 $ver	= version->new(""); # see "Quoting Rules"
	 $alpha	= version->new("1.2.3_4"); # see "Alpha	Versions"
	 $nver	= version->new(1.002);	   # see "Decimal Versions"

       Normal Form
	   For any version object which	is initialized with multiple decimal
	   places (either quoted or if possible	v-string), or initialized
	   using the qv() operator, the	stringified representation is returned
	   in a	normalized or reduced form (no extraneous zeros), and with a
	   leading 'v':

	     print $ver->normal;	 # prints as v1.2.3.4
	     print $ver->stringify;	 # ditto
	     print $ver;		 # ditto
	     print $nver->normal;	 # prints as v1.2.0
	     print $nver->stringify;	 # prints as 1.002,
					 # see "Stringification"

	   In order to preserve	the meaning of the processed version, the
	   normalized representation will always contain at least three	sub
	   terms.  In other words, the following is guaranteed to always be

	     my	$newver	= version->new($ver->stringify);
	     if	($newver eq $ver ) # always true

	   Although all	mathematical operations	on version objects are
	   forbidden by	default, it is possible	to retrieve a number which
	   corresponds to the version object through the use of	the
	   $obj->numify	method.	 For formatting	purposes, when displaying a
	   number which	corresponds a version object, all sub versions are
	   assumed to have three decimal places.  So for example:

	     print $ver->numify;	 # prints 1.002003004
	     print $nver->numify;	 # prints 1.002

	   Unlike the stringification operator,	there is never any need	to
	   append trailing zeros to preserve the correct version value.

	   The default stringification for version objects returns exactly the
	   same	string as was used to create it, whether you used "new()" or
	   "qv()", with	one exception.	The sole exception is if the object
	   was created using "qv()" and	the initializer	did not	have two
	   decimal places or a leading 'v' (both optional), then the
	   stringified form will have a	leading	'v' prepended, in order	to
	   support round-trip processing.

	   For example:

	     Initialized as	     Stringifies to
	     ==============	     ==============
	     version->new("1.2")       1.2
	     version->new("v1.2")     v1.2
	     qv("1.2.3")	       1.2.3
	     qv("v1.3.5")	      v1.3.5
	     qv("1.2")		      v1.2   ### exceptional case

	   See also UNIVERSAL::VERSION,	as this	also returns the stringified
	   form	when used as a class method.

	   IMPORTANT NOTE: There is one	exceptional cases shown	in the above
	   table where the "initializer" is not	stringwise equivalent to the
	   stringified representation.	If you use the "qv"() operator on a
	   version without a leading 'v' and with only a single	decimal	place,
	   the stringified output will have a leading 'v', to preserve the
	   sense.  See the "qv()" operator for more details.

	   IMPORTANT NOTE 2: Attempting	to bypass the normal stringification
	   rules by manually applying numify() and normal()  will sometimes
	   yield surprising results:

	     print version->new(version->new("v1.0")->numify)->normal; # v1.0.0

	   The reason for this is that the numify() operator will turn "v1.0"
	   into	the equivalent string "1.000000".  Forcing the outer version
	   object to normal() form will	display	the mathematically equivalent

	   As the example in "new()" shows, you	can always create a copy of an
	   existing version object with	the same value by the very compact:

	     $v2 = $v1->new($v1);

	   and be assured that both $v1	and $v2	will be	completely equivalent,
	   down	to the same internal representation as well as

       Comparison operators
	   Both	"cmp" and "<=>"	operators perform the same comparison between
	   terms (upgrading to a version object	automatically).	 Perl
	   automatically generates all of the other comparison operators based
	   on those two.  In addition to the obvious equalities	listed below,
	   appending a single trailing 0 term does not change the value	of a
	   version for comparison purposes.  In	other words "v1.2" and "1.2.0"
	   will	compare	as identical.

	   For example,	the following relations	hold:

	     As	Number	      As String		  Truth	Value
	     -------------    ----------------	  -----------
	     $ver >  1.0      $ver gt "1.0"	  true
	     $ver <  2.5      $ver lt		  true
	     $ver != 1.3      $ver ne "1.3"	  true
	     $ver == 1.2      $ver eq "1.2"	  false
	     $ver ==  $ver eq ""	  see discussion below

	   It is probably best to chose	either the Decimal notation or the
	   string notation and stick with it, to reduce	confusion.  Perl6
	   version objects may only support Decimal comparisons.  See also
	   "Quoting Rules".

	   WARNING: Comparing version with unequal numbers of decimal points
	   (whether explicitly or implicitly initialized), may yield
	   unexpected results at first glance.	For example, the following
	   inequalities	hold:

	     version->new(0.96)	    > version->new(0.95); # 0.960.0 > 0.950.0
	     version->new("0.96.1") < version->new(0.95); # 0.096.1 < 0.950.0

	   For this reason, it is best to use either exclusively "Decimal
	   Versions" or	"Dotted-Decimal	Versions" with multiple	decimal

       Logical Operators
	   If you need to test whether a version object	has been initialized,
	   you can simply test it directly:

	     $vobj = version->new($something);
	     if	( $vobj	)   # true only	if $something was non-blank

	   You can also	test whether a version object is an alpha version, for
	   example to prevent the use of some feature not present in the main

	     $vobj = version->new("1.2_3"); # MUST QUOTE
	     if	( $vobj->is_alpha )	  # True

       John Peacock <>


perl v5.35.5			  2021-09-26		 version::Internals(3)


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