Is there a better way to compare nullable dates?

Question

i am trying to determine if there is a difference between 2 nullable dates . . is there a more elegant ways instead of this:

  if (newDate.HasValue && (!oldDate.HasValue ||  (oldDate.HasValue && oldDate.Value.Date != mewDate.Value.Date)))

Answer 1

The C# compiler automatically lifts logical operators like == and != over nullalbe types, so you can usually compare them directly instead of checking HasValue. In this case, you can compare with != once you have checked that newDate is not null.

if(newDate.HasValue && newDate != oldDate)

It is described in the specification:

7.3.7 Lifted operators

Lifted operators permit predefined and user-defined operators that operate on non-nullable value types to also be used with nullable forms of those types.

For the equality operators == != a lifted form of an operator exists if the operand types are both non-nullable value types and if the result type is bool.The lifted form is constructed by adding a single ? modifier to each operand type. The lifted operator considers two null values equal, and a null value unequal to any non-null value. If both operands are non-null, the lifted operator unwraps the operands and applies the underlying operator to produce the bool result.