I have been reading Jimmy Nilsson's latest book titled "Applying Domain-Driven Design and Patterns With Examples in C# and .NET".  In the refactoring section, he eluded to Guarding Clauses.  He put a name to something that I have been doing in my own development without knowing that others have talked about it as a good practice.

 

To be fair, he mentioned that it originated from Martin Fowler in his refactoring book.  Either way, it felt good to know that on my own I came up with something that others would consider best practice.

 

So, just what is a guarding clause?  Well, it is where you guard your code without mixing all the code up in if statements.  That is probably way overly simplistic, but below is a simple example to follow:

 

Here is a method before being refactored to use guarding clauses.  Notice that the two if statements have nothing to do with what the method is supposed to do, they are just there to ensure the variables are correct before executing the code that needs to run.  In affect, they are guarding the functionality in order for the code to run as expected.

 

When you look at that code though, it just looks messy.  You could simplify it to this if you wanted to:

public void DoSomething()

{

   if(_someVariable != null && _someOtherVariable == "")

   {

      _someOtherVariable = _someVariable.ToString();

   }

}