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When I compile this method, there is quite a bit of resulting Intermediate Language (IL) code, which also makes performing operations on nullable types slower than performing the same operation on non-nullable types . Here is the C# equivalent of the compiler-produced IL code:
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private static Nullable<Int32> NullableCodeSize(Nullable<Int32> a, Nullable<Int32> b) { Nullable<Int32> nullable1 = a; Nullable<Int32> nullable2 = b; if (!(nullable1.HasValue & nullable2.HasValue)) { return new Nullable<Int32>(); } return new Nullable<Int32>(nullable1.GetValueOrDefault() + nullable2.GetValueOrDefault()); }
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Finally, let me point out that you can define your own value types that overload the various operators mentioned above . I discuss how to do this in the Operator Overload Methods section in 8, Methods . If you then use a nullable instance of your own value type, the compiler does the right thing and invokes your overloaded operator . For example, suppose that you have a Point value type that defines overloads for the == and != operators as follows:
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using System; internal struct Point { private Int32 m_x, m_y; public Point(Int32 x, Int32 y) { m_x = x; m_y = y; } public static Boolean operator==(Point p1, Point p2) { return (p1.m_x == p2.m_x) && (p1.m_y == p2.m_y); } public static Boolean operator!=(Point p1, Point p2) { return !(p1 == p2); } }
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At this point, you can use nullable instances of the Point type and the compiler will invoke your overloaded operators:
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internal static class public static void Point p1 = new Point p2 = new Program { Main() { Point(1, 1); Point(2, 2);
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Console.WriteLine("Are points equal " + (p1 == p2).ToString()); Console.WriteLine("Are points not equal " + (p1 != p2).ToString()); } }
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When I build and run the code above, I get the following output:
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Are points equal False Are points not equal True
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Part III Essential Types
C# s Null-Coalescing Operator
C# has an operator called the null-coalescing operator ( ), which takes two operands . If the operand on the left is not null, the operand s value is returned . If the operand on the left is null, the value of the right operand is returned . The null-coalescing operator offers a very convenient way to set a variable s default value . A cool feature of the null-coalescing operator is that it can be used with reference types as well as nullable value types . Here is some code that demonstrates the use of the nullcoalescing operator:
private static void NullCoalescingOperator() { Int32 b = null; // The line below is equivalent to: // x = (b.HasValue) b.Value : 123 Int32 x = b 123; Console.WriteLine(x); // "123" // The line below is equivalent to: // String temp = GetFilename(); // filename = (temp != null) temp : "Untitled"; String filename = GetFilename() "Untitled"; }
Some people argue that the null-coalescing operator is simply syntactic sugar for the : operator, and that the C# compiler team should not have added this operator to the language . However, the null-coalescing operator offers two significant syntactic improvements . The first is that the operator works better with expressions:
Func<String> f = () => SomeMethod() "Untitled";
This code is much easier to read and understand than the line below, which requires variable assignments and multiple statements:
Func<String> f = () => { var temp = SomeMethod(); return temp != null temp : "Untitled";};
The second improvement is that works better in composition scenarios . For example, the single line
String s = SomeMethod1() SomeMethod2() "Untitled";
is far easier to read and understand than this chunk of code:
String s; var sm1 = SomeMethod1(); if (sm1 != null) s = sm1; else { var sm2 = SomeMethod2(); if (sm2 != null) s = sm2; else s = "Untitled"; }
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