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POWhy unused event arguments require assignment?
 

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  1. POWhy unused event arguments require assignment?
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    <p>According to <a href="http://msdn.microsoft.com/en-us/library/edakx9da.aspx" rel="nofollow">C# Reference</a> </p> <blockquote> <p>"The null keyword is a literal that represents a null reference, one that does not refer to any object. null is the default value of reference-type variables'</p> </blockquote> <p>I was surprised to find out that<br> Commenting <code>e=null</code> line in the following app code (taken from the article <a href="http://softwarecafeblog.blogspot.ru/2012/06/difference-between-events-and-delegates.html" rel="nofollow">"Difference Between Events And Delegates in C#"</a>) results in compilation error: </p> <pre><code>Use of unassigned local variable 'e' </code></pre> <p>while without commenting it is compiled and run. </p> <p>I do not get: </p> <ul> <li>Where is variable <code>e</code> used? </li> <li>Is it possible to force the app to run without the dumb assigning the variable to <code>null</code>? </li> </ul> <p>f </p> <pre><code>using System; class Program { static void Main(string[] args) { DelegatesAndEvents obj = new DelegatesAndEvents(); obj.Execute(); } } public class DelegatesAndEvents { public event EventHandler MyEvent; internal void Execute() { EventArgs e; //Commenting the next line results in compilation error //Error 1 Use of unassigned local variable 'e' e = null; int sender = 15; MyEvent += MyMethod; MyEvent += MyMethod2; MyEvent(sender, e); } void MyMethod(object sender, EventArgs e) { Console.WriteLine(sender); } void MyMethod2(object sender, EventArgs e) { Console.WriteLine(sender); Console.ReadLine(); } } </code></pre> <p><strong>Update (or the comment to all answers):</strong><br> So, and I never knew it, there are to kind of nulls - one which is assigned and another which is not assigned... Funny... </p> <p>They should probably have different types, for checking:<br> if typeof(unassigned-null) then do this;<br> if typeof(assigned_null) then do that; </p>
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    1. COCheck Eric's and Mark's answers to very similar questions http://stackoverflow.com/questions/1423437/why-do-i-have-to-assign-a-value-to-an-int-in-c-sharp-when-defaults-to-0 and http://stackoverflow.com/questions/8931226/are-c-sharp-uninitalized-variables-dangerous/8933935#8933935
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    2. CO`The reason this is illegal in C# is because using an unassigned local has high likelihood of being a bug` - Eric Lippert (From link above)
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    3. CO`e` is used at the line `MyEvent(sender, e)`. The compiler does not do full analysis to determine that all subscribers ignore the `e` parameter. (Who knows. Since it's a public event, somebody else may have subscribed to `MyEvent` and that other person uses `e`.)
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      1. USRaymond Chen
 

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