I recently get to know grails and start to using it, I know that grails is a great language and it is very helpful for rapid development, but I cant understand why grails dont have a good backward compatibility, I use grails 2.3.8 and grails 2.4 for my projects but many of sample codes in the internet are 2.2 or less, and it isn't time efficient to convert them to 2.3.8 or 2.4 because there are many changes from one version to another. And some times although I do any things right and every thing must work like it works with grails 2.1 or 2.2 but some things still remains.
Am I wrong? I skipped some things that make converting version so hard?
And above all this, what are the guaranties that projects I'm developing right now will be compatible with higher versions of grails that comes in the future?
Joshua Moore is right with his answer, but I do not see it as passimistic as he does.
The grails development team is brave enough to make changes which break with the past. I consider this as a great feature - Grails does not ride dead horses.
For me, most of the changes don't seem to bee too radical. Most of the time, I skip 2-3 version and then upgrade my apps to the current stable version in less than a day. This also helps me to get to know the new features.
If you don't know how to upgrade, the safest way is to use the grails upgrade command. Just increase you version number step by step and do an upgrade and re-run your test (yes, tests help you in your upgrade process :-). If tests fail, take a look at the great changelogs and the "What new in Grails x.y?" sections of the documentation.
Often it is also helpful to compare your old grails version app with a new and empty target version project with a good comparison tool like BeyondCompare. This way you easily spot changed configurations.
Hope that helps
Update: When you are new to "all those webconcepts" you should first decide on the platform you want to work on. If it is the java ecosystem, Grails is the best webframework on the market :-) Otherwise PHP, Rails, DJango etc. could also be a match.
So if you want to learn Grails (and with Grails all those webconcepts), I would suggest to start reading the Guide which will tell you how Grails works. If you need more examples, I can suggest the "The Definitive Guide to Grails 2" published by Apress. It covers basically the same content as the guide, but it does so by walking you through a process of building a sample application.
When it comes to the samples you find on the net... as soon as you get to know the framework better, you will probaply know ho to handle the examples - but there is no silver bullet...