Nullable Value Types in Visual Studio .NET

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19 Nullable Value Types
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So now, if you want to use a nullable Int32 in your code, you can write something like this:
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Nullable<Int32> x = 5; Nullable<Int32> y = null; Console.WriteLine("x: HasValue={0}, Value={1}", Console.WriteLine("y: HasValue={0}, Value={1}",
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x.HasValue, x.Value); y.HasValue, y.GetValueOrDefault());
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When I compile and run this code, I get the following output:
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x: HasValue=True, Value=5 y: HasValue=False, Value=0
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C# s Support for Nullable Value Types
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Notice in the code that C# allows you to use fairly simple syntax to initialize the two Nullable<Int32> variables, x and y . In fact, the C# team wants to integrate nullable value types into the C# language, making them first-class citizens . To that end, C# offers an (arguably) cleaner syntax for working with nullable value types . C# allows the code to declare and initialize the x and y variables to be written using question-mark notation:
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Int32 x = 5; Int32 y = null;
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In C#, Int32 is a synonym notation for Nullable<Int32> . But C# takes this further . C# allows you to perform conversions and casts on nullable instances . And C# also supports applying operators to nullable instances . The following code shows examples of these:
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private static void ConversionsAndCasting() { // Implicit conversion from non-nullable Int32 to Nullable<Int32> Int32 a = 5; // Implicit conversion from 'null' to Nullable<Int32> Int32 b = null; // Explicit conversion from Nullable<Int32> to non-nullable Int32 Int32 c = (Int32) a; // Casting between nullable primitive types Double d = 5; // Int32->Double (d is 5.0 as a double) Double e = b; // Int32 ->Double (e is null) }
C# also allows you to apply operators to nullable instances . The following code shows examples of this:
private static void Operators() { Int32 a = 5; Int32 b = null;
Part III Essential Types
// Unary operators (+ a++; // a = 6 b = -b; // b = null ++ -! ~)
// Binary operators (+ a = a + 3; // a = 9 b = b * 3; // b = null; // if if if Equality operators (== (a == null) { /* no */ (b == null) { /* yes */ (a != b) { /* yes */
!=) } else { /* yes */ } } else { /* no */ } } else { /* no */ }
// Comparison operators (<> <= >=) if (a < b) { /* no */ } else { /* yes */ } }
Here is how C# interprets the operators:
Unary operators (+++, -, --, ! , ~) If the operand is null, the result is null . Binary operators (+, -, *, /, %, &, |, ^, <<, >>) If either operand is null, the result is null . However, an exception is made when the & and | operators are operating on Boolean operands so that the behavior of these two operators gives the same behavior as demonstrated by SQL s three-valued logic . For these two operators, if neither operand is null, the operator performs as expected, and if both operands are null, the result is null . The special behavior comes into play when just one of the operands is null . The table below lists the results produced by these two operators for all combinations of true, false, and null:
Operand1 Operand2
true false null
true
& = true | = true & = false | = true & = null | = true
false
& = false | = true & = false | = false & = false | = null
null
& = null | = true & = false | = null & = null | = null
Equality operators (==, !=) If both operands are null, they are equal . If one operand is null, they are not equal . If neither operand is null, compare the values to determine if they are equal . Relational operators (<, >, <=, >=) If either operand is null, the result is false . If neither operand is null, compare the values .
You should be aware that manipulating nullable instances does generate a lot of code . For example, see the following method:
private static Int32 NullableCodeSize(Int32 a, Int32 b) { return a + b; }
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