Essential C# Nullable types  Suggest an edit

Nullable types

Syntax

Remarks

Nullable types can represent all the values of an underlying type as well as null.

The syntax T? is shorthand for Nullable

Nullable values are System.ValueType objects actually, so they can be boxed and unboxed. Also, null value of a nullable object is not the same as null value of a reference object, it’s just a flag.

When a nullable object boxing, the null value is converted to null reference, and non-null value is converted to non-nullable underlying type.

DateTime? dt = null;
var o = (object)dt;
var result = (o == null); // is true

DateTime? dt = new DateTime(2015, 12, 11);
var o = (object)dt;
var dt2 = (DateTime)dt; // correct cause o contains DateTime value

The second rule leads to correct, but paradoxical code:

DateTime? dt = new DateTime(2015, 12, 11);
var o = (object)dt;
var type = o.GetType(); // is DateTime, not Nullable<DateTime>

In short form:

DateTime? dt = new DateTime(2015, 12, 11);
var type = dt.GetType(); // is DateTime, not Nullable<DateTime>

Table Of Contents
22 Enum
25 GUID
38 Nullable types
107 Stream
108 Timers
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