Semantic Versioning Lightning Talk, by Quinn Weaver. SF.pm 2014-05-06
=====================================================================

Perl Tie-In
-----------

Perl uses something close to semantic versioning, but you may never have
stopped to think about it.

Why Use Semantic Versioning?
----------------------------

A. Makes life easy for downstream users of your library/module/app/whatever.

1. Avoids Dependency Hell.

2. Simplifies the work of distro maintainers.
   
What is Semantic Versioning?
----------------------------

The simplified answer:

2.4.6
^ ^ ^
| | |
| | |- patch
| |
| |- minor
|
|-major

Let's look at an example. Imagine I have a library named libtoastbot,
used for controlling toasters.

Increment *patch* when you make a bug fix, like fixing a security
hole. This doesn't change the intended behavior of the system at all.
It just changes the *actual* behavior to make it (more) like
the *intended* behavior:

- libtoastbot 2.4.7: fixed a bug that caused the toaster to halt and catch fire
  when toast_darkness == 5.3

Increment *minor* when you add features, but preserve backwards compatibility.
You then reset *patch* to 0"

- libtoastbot 2.5.0: added the ability to toast bagels.

Increment *major* when you make changes that break older functionality.
Reset *minor* and *patch* to 0:

- libtoastbot 3.0.0: removed the deprecated eject_early() API call.

Why This Is Awesome
-------------------

Managing versions is a pain.

- Distributions like Debian and Red Hat are well-known for being very
  conservative, but sometimes they're too conservative.

  An old, bug-ridden version can be as bad for stability and security as an
  untested, bleeding-edge version.

- If you're writing against an API, this makes it really easy to know
  which versions to just get and which versions (major) need more
  doc reading/testing.

Semantic Versioning in Perl (Sort of)
-------------------------------------

5.18.2
^ ^^ ^
| |  |
| |  |- patch
| |
| |- major
|
|- language(!)

Semantic Versioning in PostgreSQL (Sort of)
-------------------------------------------

9.3.4
^ ^ ^
| | |
| | |- patch
| |
| |- combination of minor (new features) and major (incompatible features)
|
|- used to add emphasis to important feature releases (e.g. 9.0 and replication)
   Josh Berkus calls this "the marketing version."

Semantic Versioning Resources
-----------------------------

The spec, and an explanation:

http://semver.org/

Yes, SemVer was created by Tom Preston-Werner of GitHub harassment fame.
I can't condone his actions. But I still think SemVer is a good idea.