# class Gem::Version

The `Version` class processes string versions into comparable values. A version string should normally be a series of numbers separated by periods. Each part (digits separated by periods) is considered its own number, and these are used for sorting. So for instance, 3.10 sorts higher than 3.2 because ten is greater than two.

If any part contains letters (currently only a-z are supported) then that version is considered prerelease. Versions with a prerelease part in the Nth part sort less than versions with N-1 parts. Prerelease parts are sorted alphabetically using the normal Ruby string sorting rules. If a prerelease part contains both letters and numbers, it will be broken into multiple parts to provide expected sort behavior (1.0.a10 becomes 1.0.a.10, and is greater than 1.0.a9).

Prereleases sort between real releases (newest to oldest):

1. 1.0

2. 1.0.b1

3. 1.0.a.2

4. 0.9

If you want to specify a version restriction that includes both prereleases and regular releases of the 1.x series this is the best way:

    s.add_dependency 'example', '>= 1.0.0.a', '< 2.0.0'

## How Software Changes¶ ↑

Users expect to be able to specify a version constraint that gives them some reasonable expectation that new versions of a library will work with their software if the version constraint is true, and not work with their software if the version constraint is false. In other words, the perfect system will accept all compatible versions of the library and reject all incompatible versions.

Libraries change in 3 ways (well, more than 3, but stay focused here!).

1. The change may be an implementation detail only and have no effect on the client software.

2. The change may add new features, but do so in a way that client software written to an earlier version is still compatible.

3. The change may change the public interface of the library in such a way that old software is no longer compatible.

Some examples are appropriate at this point. Suppose I have a Stack class that supports a `push` and a `pop` method.

### Examples of Category 1 changes:¶ ↑

- Switch from an array based implementation to a linked-list based implementation.

- Provide an automatic (and transparent) backing store for large stacks.

### Examples of Category 2 changes might be:¶ ↑

- Add a `depth` method to return the current depth of the stack.

- Add a `top` method that returns the current top of stack (without changing the stack).

- Change `push` so that it returns the item pushed (previously it had no usable return value).

### Examples of Category 3 changes might be:¶ ↑

- Changes `pop` so that it no longer returns a value (you must use `top` to get the top of the stack).

- Rename the methods to `push_item` and `pop_item`.

## RubyGems `Rational` Versioning¶ ↑

- Versions shall be represented by three non-negative integers, separated by periods (e.g. 3.1.4). The first integers is the “major” version number, the second integer is the “minor” version number, and the third integer is the “build” number.

- A category 1 change (implementation detail) will increment the build number.

- A category 2 change (backwards compatible) will increment the minor version number and reset the build number.

- A category 3 change (incompatible) will increment the major build number and reset the minor and build numbers.

- Any “public” release of a gem should have a different version. Normally that means incrementing the build number. This means a developer can generate builds all day long, but as soon as they make a public release, the version must be updated.

### Examples¶ ↑

Let’s work through a project lifecycle using our Stack example from above.

`Version` 0.0.1

  The initial Stack class is release.

`Version` 0.0.2

  Switched to a linked=list implementation because it is cooler.

`Version` 0.1.0

  Added a `depth` method.

`Version` 1.0.0

  Added `top` and made `pop` return nil (`pop` used to return the old top item).

`Version` 1.1.0

  `push` now returns the value pushed (it used it return nil).

`Version` 1.1.1

  Fixed a bug in the linked list implementation.

`Version` 1.1.2

  Fixed a bug introduced in the last fix.

Client A needs a stack with basic push/pop capability. They write to the original interface (no `top`), so their version constraint looks like:

    gem 'stack', '>= 0.0'

Essentially, any version is OK with Client A. An incompatible change to the library will cause them grief, but they are willing to take the chance (we call Client A optimistic).

Client B is just like Client A except for two things: (1) They use the `depth` method and (2) they are worried about future incompatibilities, so they write their version constraint like this:

    gem 'stack', '~> 0.1'

The `depth` method was introduced in version 0.1.0, so that version or anything later is fine, as long as the version stays below version 1.0 where incompatibilities are introduced. We call Client B pessimistic because they are worried about incompatible future changes (it is OK to be pessimistic!).

## Preventing `Version` Catastrophe:¶ ↑

From: www.zenspider.com/ruby/2008/10/rubygems-how-to-preventing-catastrophe.html

Let’s say you’re depending on the fnord gem version 2.y.z. If you specify your dependency as “>= 2.0.0” then, you’re good, right? What happens if fnord 3.0 comes out and it isn’t backwards compatible with 2.y.z? Your stuff will break as a result of using “>=”. The better route is to specify your dependency with an “approximate” version specifier (“~>”). They’re a tad confusing, so here is how the dependency specifiers work:

    Specification From  ... To (exclusive)
    ">= 3.0"      3.0   ... &infin;
    "~> 3.0"      3.0   ... 4.0
    "~> 3.0.0"    3.0.0 ... 3.1
    "~> 3.5"      3.5   ... 4.0
    "~> 3.5.0"    3.5.0 ... 3.6
    "~> 3"        3.0   ... 4.0

For the last example, single-digit versions are automatically extended with a zero to give a sensible result.

### Public Class Methods

correct? (version)
Source

    # File lib/rubygems/version.rb, line 173
    def self.correct?(version)
      nil_versions_are_discouraged! if version.nil?

      ANCHORED_VERSION_PATTERN.match?(version.to_s)
    end

True if the `version` string matches RubyGems’ requirements.

create (input)
Source

    # File lib/rubygems/version.rb, line 187
    def self.create(input)
      if self === input # check yourself before you wreck yourself
        input
      elsif input.nil?
        nil_versions_are_discouraged!

        nil
      else
        new input
      end
    end

Factory method to create a `Version` object. Input may be a `Version` or a `String`. Intended to simplify client code.

    ver1 = Version.create('1.3.17')   # -> (Version object)
    ver2 = Version.create(ver1)       # -> (ver1)
    ver3 = Version.create(nil)        # -> nil

new (version)
Source

    # File lib/rubygems/version.rb, line 221
    def initialize(version)
      unless self.class.correct?(version)
        raise ArgumentError, "Malformed version number string #{version}"
      end

      # If version is an empty string convert it to 0
      version = 0 if version.is_a?(String) && /\A\s*\Z/.match?(version)

      @version = version.to_s

      # optimization to avoid allocation when given an integer, since we know
      # it's to_s won't have any spaces or dashes
      unless version.is_a?(Integer)
        @version = @version.strip
        @version.gsub!("-",".pre.")
      end
      @version = -@version
      @segments = nil
    end

Constructs a `Version` from the `version` string. A version string is a series of digits or ASCII letters separated by dots.

### Private Class Methods

nil_versions_are_discouraged! ()
Source

    # File lib/rubygems/version.rb, line 209
    def self.nil_versions_are_discouraged!
      unless Gem::Deprecate.skip
        warn "nil versions are discouraged and will be deprecated in Rubygems 4"
      end
    end

### Public Instance Methods

<=> (other)
Source

    # File lib/rubygems/version.rb, line 360
    def <=>(other)
      return self <=> self.class.new(other) if (String === other) && self.class.correct?(other)

      return unless Gem::Version === other
      return 0 if @version == other.version || canonical_segments == other.canonical_segments

      lhsegments = canonical_segments
      rhsegments = other.canonical_segments

      lhsize = lhsegments.size
      rhsize = rhsegments.size
      limit  = (lhsize > rhsize ? lhsize : rhsize) - 1

      i = 0

      while i <= limit
        lhs = lhsegments[i] || 0
        rhs = rhsegments[i] || 0
        i += 1

        next      if lhs == rhs
        return -1 if String  === lhs && Numeric === rhs
        return  1 if Numeric === lhs && String  === rhs

        return lhs <=> rhs
      end

      0
    end

Compares this version with `other` returning -1, 0, or 1 if the other version is larger, the same, or smaller than this one. Attempts to compare to something that’s not a `Gem::Version` or a valid version `String` return `nil`.

approximate_recommendation ()
Source

    # File lib/rubygems/version.rb, line 342
    def approximate_recommendation
      segments = self.segments

      segments.pop    while segments.any? {|s| String === s }
      segments.pop    while segments.size > 2
      segments.push 0 while segments.size < 2

      recommendation = "~> #{segments.join(".")}"
      recommendation += ".a" if prerelease?
      recommendation
    end

A recommended version for use with a ~> Requirement.

bump ()
Source

    # File lib/rubygems/version.rb, line 247
    def bump
      @@bump[self] ||= begin
                         segments = self.segments
                         segments.pop while segments.any? {|s| String === s }
                         segments.pop if segments.size > 1

                         segments[-1] = segments[-1].succ
                         self.class.new segments.join(".")
                       end
    end

Return a new version object where the next to the last revision number is one greater (e.g., 5.3.1 => 5.4).

Pre-release (alpha) parts, e.g, 5.3.1.b.2 => 5.4, are ignored.

canonical_segments ()
Source

    # File lib/rubygems/version.rb, line 391
    def canonical_segments
      @canonical_segments ||= begin
        # remove trailing 0 segments, using dot or letter as anchor
        # may leave a trailing dot which will be ignored by partition_segments
        canonical_version = @version.sub(/(?<=[a-zA-Z.])[.0]+\z/, "")
        # remove 0 segments before the first letter in a prerelease version
        canonical_version.sub!(/(?<=\.|\A)[0.]+(?=[a-zA-Z])/, "") if prerelease?
        partition_segments(canonical_version)
      end
    end

remove trailing zeros segments before first letter or at the end of the version

eql? (other)
Source

    # File lib/rubygems/version.rb, line 262
    def eql?(other)
      self.class === other && @version == other.version
    end

A `Version` is only eql? to another version if it’s specified to the same precision. `Version` “1.0” is not the same as version “1”.

freeze ()
Source

    # File lib/rubygems/version.rb, line 402
    def freeze
      prerelease?
      _segments
      canonical_segments
      super
    end

Calls superclass method `Object#freeze`
marshal_dump ()
Source

    # File lib/rubygems/version.rb, line 282
    def marshal_dump
      [@version]
    end

Dump only the raw version string, not the complete object. It’s a string for backwards (RubyGems 1.3.5 and earlier) compatibility.

marshal_load (array)
Source

    # File lib/rubygems/version.rb, line 290
    def marshal_load(array)
      string = array[0]
      raise TypeError, "wrong version string" unless string.is_a?(String)

      initialize string
    end

Load custom marshal format. It’s a string for backwards (RubyGems 1.3.5 and earlier) compatibility.

prerelease? ()
Source

    # File lib/rubygems/version.rb, line 310
    def prerelease?
      unless instance_variable_defined? :@prerelease
        @prerelease = /[a-zA-Z]/.match?(version)
      end
      @prerelease
    end

A version is considered a prerelease if it contains a letter.

release ()
Source

    # File lib/rubygems/version.rb, line 325
    def release
      @@release[self] ||= if prerelease?
        segments = self.segments
        segments.pop while segments.any? {|s| String === s }
        self.class.new segments.join(".")
      else
        self
      end
    end

The release for this version (e.g. 1.2.0.a -> 1.2.0). Non-prerelease versions return themselves.

to_s ()
Alias for: version
version ()
Source

    # File lib/rubygems/version.rb, line 164
    def version
      @version
    end

A string representation of this `Version`.

Also aliased as: to_s

### Protected Instance Methods

_segments ()
Source

    # File lib/rubygems/version.rb, line 411
    def _segments
      # segments is lazy so it can pick up version values that come from
      # old marshaled versions, which don't go through marshal_load.
      # since this version object is cached in @@all, its @segments should be frozen
      @segments ||= partition_segments(@version)
    end

partition_segments (ver)
Source

    # File lib/rubygems/version.rb, line 418
    def partition_segments(ver)
      ver.scan(/\d+|[a-z]+/i).map! do |s|
        /\A\d/.match?(s) ? s.to_i : -s
      end.freeze
    end