12: Delegates and Lambda Expressions in Visual C#

Print QR in Visual C# 12: Delegates and Lambda Expressions
12: Delegates and Lambda Expressions
QR Code JIS X 0510 Creation In Visual C#.NET
Using Barcode generation for .NET Control to generate, create Quick Response Code image in VS .NET applications.
Since the delegate definitions in Listing 1213 are generic, it is possible to use them instead of defining a custom delegate For example, rather than declaring the ComparisonHandler delegate type, code could simply declare ComparisonHandler delegates using Func<int, int, bool> The last type parameter of Func is always the return type of the delegate The earlier type parameters correspond in sequence to the type of delegate parameters In the case of ComparisonHandler, the return is bool (the last type parameter of the Func declaration) and the type arguments int and int correspond with the first and second parameters of ComparisonHandler In many cases, the inclusion of Func delegates in the NET 35 Framework eliminates the necessity to define delegates You should use SystemAction, or one of the generic versions, for delegates that have no return (TResult) and that take no parameters However, you should still declare delegate types when such a type would simplify coding with the delegate For example, continuing to use the ComparisonHandler provides a more explicit indication of what the delegate is used for, whereas Func<int, int, bool> provides nothing more than an understanding of the method signature Evaluation about whether to declare a delegate is still meaningful and includes considerations such as whether the name of the delegate identifier is sufficient for indicating intent, whether the delegate type name would clarify its use, and whether the use of a NET 35 type will limit the use of the assembly to NET 35 clients unnecessarily Note that even though you can use a generic Func delegate in place of an explicitly defined delegate, the types are not compatible You cannot assign one delegate type to a variable of another delegate type even if the type parameters match For example, you cannot assign a ComparisonHandler variable to a Func<int, int, bool> variable or pass them interchangeably as parameters even though both represent signatures for a delegate that takes two int parameters and returns a bool However, notice the type parameter modifiers decorating the delegates in Listing 1213 These do allow for some degree of casting between them, thanks to the variance support added in C# 40 Consider the following contravariant example: Because void Action<in T>(T arg) has the in type parameter decorator, it is possible to assign type Action<string> an object
Barcode Creation In C#
Using Barcode generation for VS .NET Control to generate, create barcode image in .NET framework applications.
System-Defined Delegates: Func<>
QR Code ISO/IEC18004 Maker In .NET
Using Barcode drawer for ASP.NET Control to generate, create QR Code 2d barcode image in ASP.NET applications.
of type Action<object> In other words, any methods with a void return and an object parameter will implicitly cast to the more restrictive delegate type that only allows parameters of type string Similarly with covariance and a Func delegate since TResult Func<out TResult>() includes the out type parameter modifier on TResult, it is possible to implicitly assign a Func<object> variable the value of a Func<string> (See Listing 1214)
QR Encoder In Visual Studio .NET
Using Barcode printer for .NET Control to generate, create QR Code ISO/IEC18004 image in Visual Studio .NET applications.
Listing 1214: Using Variance for Delegates
Denso QR Bar Code Maker In Visual Basic .NET
Using Barcode encoder for .NET Control to generate, create QR image in Visual Studio .NET applications.
// Contravariance Action<object> broadAction = delegate(object data) { ConsoleWriteLine(data); }; Action<string> narrowAction = broadAction; // Contravariance Func<string> narrowFunction = delegate() { return ConsoleReadLine(); }; Func<object> broadFunction = narrowFunction; // Contravariance & Covariance Combined Func<object, string> func1 = delegate(object data) { return dataToString(); }; Func<string, object> func2 = func1;
Encoding Barcode In Visual C#
Using Barcode generator for Visual Studio .NET Control to generate, create bar code image in VS .NET applications.
The last part of the listing combines both variance concepts into a single example, demonstrating how they can occur simultaneously if both in and out type parameters are involved The need for variance support within these generic delegates was a key contributing factor for why C# now includes the feature2
Create Barcode In C#
Using Barcode printer for VS .NET Control to generate, create barcode image in .NET framework applications.
2 The other was support for covariance to IEnumerable<out T>
Code 39 Extended Maker In C#
Using Barcode creator for VS .NET Control to generate, create ANSI/AIM Code 39 image in .NET applications.
12: Delegates and Lambda Expressions
Code 128 Code Set A Drawer In C#
Using Barcode generator for .NET Control to generate, create Code 128 Code Set A image in .NET framework applications.
Lambda Expressions
Data Matrix ECC200 Printer In Visual C#.NET
Using Barcode encoder for VS .NET Control to generate, create Data Matrix image in VS .NET applications.
Introduced in C# 30, lambda expressions are a more succinct syntax of anonymous functions than anonymous methods, where anonymous functions is a general term that includes both lambda expressions and anonymous methods Lambda expressions are themselves broken into two types: statement lambdas and expression lambdas Figure 122 shows the hierarchical relationship between the terms
UPC A Maker In .NET
Using Barcode encoder for ASP.NET Control to generate, create GTIN - 12 image in ASP.NET applications.
Read UCC - 12 In .NET
Using Barcode recognizer for VS .NET Control to read, scan read, scan image in .NET framework applications.
Encode Data Matrix In Visual Basic .NET
Using Barcode encoder for Visual Studio .NET Control to generate, create Data Matrix image in .NET framework applications.
Create EAN13 In .NET Framework
Using Barcode encoder for Visual Studio .NET Control to generate, create GTIN - 13 image in .NET framework applications.
Bar Code Encoder In .NET
Using Barcode encoder for ASP.NET Control to generate, create barcode image in ASP.NET applications.
Drawing Code 39 Extended In Visual Basic .NET
Using Barcode creation for .NET Control to generate, create Code39 image in Visual Studio .NET applications.