Question

Could someone explain why this works in C#.NET 2.0:

    Nullable<DateTime> foo;     if (true)         foo = null;     else         foo = new DateTime(0); 

…but this doesn’t:

    Nullable<DateTime> foo;     foo = true ? null : new DateTime(0); 

The latter form gives me an compile error ‘Type of conditional expression cannot be determined because there is no implicit conversion between ‘<null>’ and ‘System.DateTime’.’

Not that I can’t use the former, but the second style is more consistent with the rest of my code.

Answer 1

The compiler is telling you that it doesn’t know how convert null into a DateTime.

The solution is simple:

DateTime? foo; foo = true ? (DateTime?)null : new DateTime(0); 

Note that Nullable<DateTime> can be written DateTime? which will save you a bunch of typing.