Today I had a discussion about coding guidelines and in particular about the size of a class, the number of methods in a class and the number of lines of code per class. What is right?

Ofcourse a little search on Google revealed millions of hits. Some of the more useful ones were:

• Java Code Guidelines: http://www.horstmann.com/bigj/style.html
• C# Coding Style Guide: http://www.csharpfriends.com/Articles/getArticle.aspx?articleID=336
• IDesign C# Coding Standards: http://www.idesign.net/idesign/download/IDesign%20CSharp%20Coding%20Standard.zip
• The Philips Guidelines: http://www.tiobe.com/standards/gemrcsharpcs.pdf

Most standards don't say much about the size of a class, the number of methods in a class and the number of lines of code per class. The few that do say something come fairly close.

Here's the sum of guidelines that I think I'll stick by:

1. A source file should only contain one class
2. A method should be no more than 30 lines of code, excluding blank lines and comments
3. A source file should contain no more than 1000 lines, including blanks and comments
4. An interface should have no more than 10 methods, excluding overloads, ie. the combination of overloads counts as one methods
5. C# 2.0 allows partial classes:
• a source file should only contain one partial class
• don't split the implementation of an interface across multiple files
• for large classes split the implementation of interfaces and implement one interface per file
• Filename:  <classname>.<interfacename>.cs
• if you have a class which implements one interace, but has a lot of private methods, then create a partial class with just the private methods:
• Filename: <classname>.private.cs

Ad 2.
This is the average I found and seems to make sense, since this means that with one look at the screen your brain can absorb the whole method.

Ad 3.
I'm not convinced this is a very important rule. Having 2000 lines of code in one file or spread across two classes in two files doesn't really make that big a difference to me. See also ad 5.

Ad 4.
This is mainly because of Intellisense. Ten methods will provide optimum use of Intellisense.

Ad 5.
Partial classes are great!