The this keyword and double question mark (??) confuse me

Possible Duplicate:
What do two question marks together mean in C#?

Is this a new feature added to C# 3.x ?

eg

public class HttpRequests
{
    public string GetHtmlContent(this HttpRequest myRequest)
    {            
       //do something
       return retStr ?? (retStr=new GetHtmlStr(urlStr));
    }
}

The this and ?? are strange to me since I have not updated my know of C# for years. I know C# 2.x.

For conditional if and return value ie

return a == 0 ? a:b;

yes I can understand what this is. Could someone please explain ?

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?? - null coalescing operator introduced with .Net 2.0

this in method -> specifies extension method on existing type, introduced with C# 3.0

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这是一个null-coalising操作符，请参阅MSDN解释

---

GetHtmlContent(this HttpRequest myRequest)

Well this infers it to be an Extension method but does your code compile since your class is not static

When the first parameter of a method includes the this modifier, that method is said to be an extension method. Extension methods can only be declared in non-generic, non-nested static classes. The first parameter of an extension method can have no modifiers other than this, and the parameter type cannot be a pointer type.

Also ?? is a null coalescing operator

string something = maybenull ?? "I cannot be null";

so when maybenull object is null you get the other string assigned to your string.

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