What do two question marks together mean in C#?

Question

Ran across this line of code:

FormsAuth = formsAuth ?? new FormsAuthenticationWrapper();

What do the two question marks mean, is it some ki

Answer 1

Some of the examples here of getting values using coalescing are inefficient.

What you really want is:

return _formsAuthWrapper = _formsAuthWrapper ?? new FormsAuthenticationWrapper();

or

return _formsAuthWrapper ?? (_formsAuthWrapper = new FormsAuthenticationWrapper());

This prevents the object from being recreated every time. Instead of the private variable remaining null and a new object getting created on every request, this ensures the private variable is assigned if the new object is created.