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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

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:

Examples of Category 2 changes might be:

Examples of Category 3 changes might be:

RubyGems Rational Versioning

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. 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

Attributes

version[R]

A string representation of this Version.

Public Class Methods

correct?(version) click to toggle source

True if the version string matches RubyGems’ requirements.

     # File lib/rubygems/version.rb, line 160
160:   def self.correct? version
161:     version.to_s =~ ANCHORED_VERSION_PATTERN
162:   end
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 lib/rubygems/version.rb, line 172
172:   def self.create input
173:     if input.respond_to? :version then
174:       input
175:     elsif input.nil? then
176:       nil
177:     else
178:       new input
179:     end
180:   end
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 lib/rubygems/version.rb, line 186
186:   def initialize version
187:     raise ArgumentError, "Malformed version number string #{version}" unless
188:       self.class.correct?(version)
189: 
190:     @version = version.to_s
191:     @version.strip!
192:   end

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. Attempts to compare to something that’s not a Gem::Version return nil.

     # File lib/rubygems/version.rb, line 293
293:   def <=> other
294:     return unless Gem::Version === other
295:     return 0 if @version == other.version
296: 
297:     lhsegments = segments
298:     rhsegments = other.segments
299: 
300:     lhsize = lhsegments.size
301:     rhsize = rhsegments.size
302:     limit  = (lhsize > rhsize ? lhsize : rhsize) - 1
303: 
304:     i = 0
305: 
306:     while i <= limit
307:       lhs, rhs = lhsegments[i] || 0, rhsegments[i] || 0
308:       i += 1
309: 
310:       next      if lhs == rhs
311:       return 1 if String  === lhs && Numeric === rhs
312:       return  1 if Numeric === lhs && String  === rhs
313: 
314:       return lhs <=> rhs
315:     end
316: 
317:     return 0
318:   end
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.b.2 => 5.4, are ignored.

     # File lib/rubygems/version.rb, line 200
200:   def bump
201:     segments = self.segments.dup
202:     segments.pop while segments.any? { |s| String === s }
203:     segments.pop if segments.size > 1
204: 
205:     segments[1] = segments[1].succ
206:     self.class.new segments.join(".")
207:   end
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 lib/rubygems/version.rb, line 213
213:   def eql? other
214:     self.class === other and @version == other.version
215:   end
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 lib/rubygems/version.rb, line 229
229:   def marshal_dump
230:     [version]
231:   end
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 lib/rubygems/version.rb, line 237
237:   def marshal_load array
238:     initialize array[0]
239:   end
prerelease?() click to toggle source

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

     # File lib/rubygems/version.rb, line 244
244:   def prerelease?
245:     @prerelease ||= @version =~ /[a-zA-Z]/
246:   end
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 lib/rubygems/version.rb, line 256
256:   def release
257:     return self unless prerelease?
258: 
259:     segments = self.segments.dup
260:     segments.pop while segments.any? { |s| String === s }
261:     self.class.new segments.join('.')
262:   end
spermy_recommendation() click to toggle source

A recommended version for use with a ~> Requirement.

     # File lib/rubygems/version.rb, line 277
277:   def spermy_recommendation
278:     segments = self.segments.dup
279: 
280:     segments.pop    while segments.any? { |s| String === s }
281:     segments.pop    while segments.size > 2
282:     segments.push 0 while segments.size < 2
283: 
284:     "~> #{segments.join(".")}"
285:   end

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