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copied!<h1>Question 1</h1> <p>The <code>??</code> is called the <a href="http://msdn.microsoft.com/en-us/library/ms173224.aspx" rel="nofollow noreferrer"><strong>null-coalescing operator</strong></a>, and is a very useful feature of C# 2.0 onwards.</p> <p>In your case,</p> <pre><code>FormsAuth = formsAuth ?? new FormsAuthenticationWrapper(); </code></pre> <p>simply means "assign <code>formsAuth</code> to <code>FormsAuth</code> unless it is null, in which case assign <code>new FormsAuthenticationWrapper()</code>". It's basically a way of preventing null references in your code. You can also think of it as a shortcut for the following conditional expression:</p> <pre><code>FormsAuth = formsAuth != null ? formsAuth : new FormsAuthenticationWrapper(); </code></pre> <h1>Question 2</h1> <p>The use of <code>this(null, null)</code> is called <a href="http://www.yoda.arachsys.com/csharp/constructors.html" rel="nofollow noreferrer"><strong>constructor chaining</strong></a>. All this means is that that the constructor in the same class (hence <code>this</code>, as opposed to <code>base</code> for the parent class) that takes two parameters, should be called before the body of the constructor is executed.</p> <p>Overloading constructors is a common practice to make it easier for the developer to create new objects when they just want to use the default properties/settings.</p> <h1>Question 3</h1> <p>As others have mentioned, this really belongs as a separate question. Unlike the previous two, it's much more specific to the context/your code, rather than language features of C#.</p> <h1>Update</h1> <p>Ok, what I've done now is actually rewritten the two constructors here, since I think putting them in another (virtually equivalent) form might be a bit clearer, and is probably better design practice too. The null coalescing operator isn't necessary here.</p> <pre><code>public AuthenticationController() : this(new FormsAuthenticationWrapper(), Membership.Provider) { } public AuthenticationController(IFormsAuthentication formsAuth, MembershipProvider provider) { this.FormsAuth = formsAuth; this.Provider = provider; } </code></pre> <p>In this form, it should be obvious that the constructor that takes two parameters simply assigns the class variables to the values of the arguments. The parameterless constructor (often called the <em>default</em> constructor) simply creates a new object using the <em>default</em> <code>FormsAuth</code> and <code>Provider</code> objects, which are specified via <em>constructor chaining</em>.</p>

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