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copied!<p>One approach which I have used a lot is the <a href="http://en.wikipedia.org/wiki/Null_Object_pattern" rel="nofollow">null object pattern.</a> For example, if a have a factory class which returns different implementations of an interface based on an argument, and the provided argument is not mapped to any of the implementations, I would return a NullObject, e.g.</p> <pre><code> public interface IFoo{ void Bar(); } public class NullFoo{ public void Bar(){ //null behaviour } } public class FooFactory{ public IFoo CreateFoo(int i){ switch(i){ case 1: return new OneFoo(); break; case 2: return new TwoFoo(); break; default: return new NullFoo(); break; } } } </code></pre> <p>When I want get an <code>IFoo</code> from <code>CreateFoo</code>, I don't have to check whether the returned object is null.</p> <p>Obviously, this is just one of the many approaches. There is no "one size fits all" since null can mean different things.</p> <p>Another way to guard against null arguments is to use <a href="http://msdn.microsoft.com/en-us/magazine/ee236408.aspx#id0070015" rel="nofollow">CodeContract preconditions</a>. e.g.</p> <pre><code> public void Foo(Bar x){ Contract.Requires<ArgumentNullException>( x != null, "x" ); //access x } </code></pre> <p>Using Code Contracts allows you to run static code analysis against your code and catch bugs such as <code>Foo(null)</code>. (<a href="http://msdn.microsoft.com/en-us/magazine/hh335064.aspx" rel="nofollow">more here</a>)</p> <p>One more why to do it would be to use a very simple generic extension method:</p> <pre><code>public static class Ex { public static void EnsureNotNull<T>(this T t, string argName) where T:class { if(t == null) { throw new ArgumentNullException(argName); } } } </code></pre> <p>Then you can check your arguments like this:</p> <pre><code> public void Foo(Bar x, Bar y){ x.EnsureNotNull("x"); y.EnsureNotNull("y"); } </code></pre>

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