Extended maintenance of Ruby versions 1.8.7 and 1.9.2 ended on July 31, 2014. Read more

In Files

  • rubygems/requirement.rb
  • rubygems/version.rb

Class/Module Index [+]



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.

Prereleases sort between real releases (newest to oldest):

  1. 1.0

  2. 1.0.b

  3. 1.0.a

  4. 0.9

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 for himself, but as soon as he/she makes a public release, the version must be updated.


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. He writes to the original interface (no top), so his version constraint looks like:

gem 'stack', '~> 0.0'

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

Client B is just like Client A except for two things: (1) He uses the depth method and (2) he is worried about future incompatibilities, so he writes his 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 he is worried about incompatible future changes (it is OK to be pessimistic!).

Preventing Version Catastrophe:

From: blog.zenspider.com/2008/10/rubygems-howto-preventing-cata.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 a “spermy” version specifier. They’re a tad confusing, so here is how the dependency specifiers work:

Specification From  ... To (exclusive)
">= 3.0"      3.0   ... ∞
"~> 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

Public Class Methods

correct?(version) click to toggle source

True if the version string matches RubyGems’ requirements.

               # File rubygems/version.rb, line 155
def self.correct? version
create(input) click to toggle source

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
               # File rubygems/version.rb, line 167
def self.create input
  if input.respond_to? :version then
  elsif input.nil? then
    new input
new(version) click to toggle source

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

               # File rubygems/version.rb, line 181
def initialize version
  raise ArgumentError, "Malformed version number string #{version}" unless

  @version = version.to_s

  segments # prime @segments

Public Instance Methods

<=>(other) click to toggle source

Compares this version with other returning -1, 0, or 1 if the other version is larger, the same, or smaller than this one.

               # File rubygems/version.rb, line 290
def <=> other
  return   1 unless other # HACK: comparable with nil? why?
  return nil unless self.class === other

  lhsize = segments.size
  rhsize = other.segments.size
  limit  = (lhsize > rhsize ? lhsize : rhsize) - 1

  0.upto(limit) do |i|
    lhs, rhs = segments[i] || 0, other.segments[i] || 0

    return  -1         if String  === lhs && Numeric === rhs
    return   1         if Numeric === lhs && String  === rhs
    return lhs <=> rhs if lhs != rhs

  return 0
bump() click to toggle source

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.b2 => 5.4, are ignored.

               # File rubygems/version.rb, line 197
def bump
  segments = self.segments.dup
  segments.pop while segments.any? { |s| String === s }
  segments.pop if segments.size > 1

  segments[-1] = segments[-1].succ
  self.class.new segments.join(".")
eql?(other) click to toggle source

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”.

               # File rubygems/version.rb, line 210
def eql? other
  self.class === other and segments == other.segments
marshal_dump() click to toggle source

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

               # File rubygems/version.rb, line 226
def marshal_dump
marshal_load(array) click to toggle source

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

               # File rubygems/version.rb, line 234
def marshal_load array
  initialize array[0]
prerelease?() click to toggle source

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

               # File rubygems/version.rb, line 241
def prerelease?
  @prerelease ||= segments.any? { |s| String === s }
release() click to toggle source

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

               # File rubygems/version.rb, line 253
def release
  return self unless prerelease?

  segments = self.segments.dup
  segments.pop while segments.any? { |s| String === s }
  self.class.new segments.join('.')
spermy_recommendation() click to toggle source

A recommended version for use with a ~> Requirement.

               # File rubygems/version.rb, line 276
def spermy_recommendation
  segments = self.segments.dup

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

  "~> #{segments.join(".")}"