How to decide between C# static and non-static methods?

Question

[Edit]

My original-question was \"Why to decide between static and non-static? Both do the same...\"

Unfortunately it was edited to a C#-specific question wh

Answer 1

Here we go.

First off:

So I tend to use static methods very often (to be independent from a concrete instance - independency is always good thing).

Quite the contrary: when using static methods you're very dependent on the concrete instance.

As far as your Document is concerned, I'd go neither way. You've listed all responsibilities of Document class, which includes aggregation of data, saving itself to the database plus operations on pages and copying.

This is way to much. Per SRP, each "module" (here "module" used as a catch-all term) should have only one reason to change. Your Document has lots of responsibilities, hence it has a whole slew of reasons to change. This is no good.

With that in mind, I'd move all logic to other classes with strictly defined responsibilities. A more or less accepted criterion of what to move was introduced, I believe, by either Herb Sutter or Andrei Alexandrescu, an is as follows: all operations (think methods) that can be performed with an object through its public contract should be moved outside the object in question.

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