Func ＜ T, tresult ＞ Commission - learning record

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a key

Namespace :System
Assembly :mscorlib.dll, System.Runtime.dll
A value must be returned

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Tips ： The following is the main body of this article , The following cases can be used for reference

One 、Func<T,TResult> What is a commission ？

Encapsulate a method , The method has one parameter , And returned by TResult The value of the type specified by the parameter

public delegate TResult Func<in T,out TResult>(T arg);

T The parameter types of the methods encapsulated for this delegate .
TResult The return value type of the method encapsulated for this delegate .

Two 、 Example

1. Routine usage

The following example demonstrates how to declare and use Func<T,TResult> entrust . This example declares a Func<T,TResult> Variable , And assign a lambda expression , This expression converts the characters in the string to uppercase . The delegate that encapsulates this method is then passed to Enumerable.Select Method , To change the string in the string array to uppercase .

The code is as follows （ Example ）：

// Declare a Func variable and assign a lambda expression to the
// variable. The method takes a string and converts it to uppercase.
Func<string, string> selector = str => str.ToUpper();

// Create an array of strings.
string[] words = {
     "orange", "apple", "Article", "elephant" };
// Query the array and select strings according to the selector method.
IEnumerable<String> aWords = words.Select(selector);

// Output the results to the console.
foreach (String word in aWords)
    Console.WriteLine(word);

/* This code example produces the following output: ORANGE APPLE ARTICLE ELEPHANT */

annotation ： Use this delegate to represent a method , This method can be passed as a parameter , Without explicitly declaring a custom delegate . The encapsulated method must correspond to the method signature defined by this delegate . It means , The encapsulated method must have a parameter passed to it by value , And must return a value . To reference a method , This method takes one parameter and returns void Methods Function , Use generics instead Action entrust .

2. lambda Expression assigned to Func<T,TResult> entrust

The code is as follows （ Example ）：

Func<string, string> convert = s => s.ToUpper();

string name = "Dakota";
Console.WriteLine(convert(name));

// This code example produces the following output:
//
// DAKOTA

Lambda The underlying type of an expression is a generic type Func entrust . such , Can will lambda The expression is passed as an argument , Instead of explicitly assigning it to delegates . To be specific , Because there are many types of methods in the namespace System.Linq There are Func<T,TResult> Parameters , So you can pass these methods to lambda expression , Without explicit instantiation Func<T,TResult> entrust .

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summary

Func<T1,T2,T3,T4,T5,T6,T7,T8,TResult> entrust

public delegate TResult Func<in T1,in T2,in T3,in T4,in T5,in T6,in T7,in T8,out TResult>(T1 arg1, T2 arg2, T3 arg3, T4 arg4, T5 arg5, T6 arg6, T7 arg7, T8 arg8);

The method has eight parameters , And back to TResult The value of the type specified by the parameter . also 9-16 Parameters , Simply put, a delegate with a return value , A value must be returned . In daily use , I'm familiar with it after using it twice , Don't try to remember