Class | Gem::Version |
In: |
lib/rubygems/version.rb
|
Parent: | Object |
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):
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!).
Some examples are appropriate at this point. Suppose I have a Stack class that supports a push and a pop method.
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!).
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
version | -> | to_s |
version | [R] | A string representation of this Version. |
Constructs a Version from the version string. A version string is a series of digits or ASCII letters separated by dots.
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.
Dump only the raw version string, not the complete object. It‘s a string for backwards (RubyGems 1.3.5 and earlier) compatibility.
The release for this version (e.g. 1.2.0.a -> 1.2.0). Non-prerelease versions return themselves.