Differences between Func & lt; T & gt; and Action & lt; T & gt;: funcaction

Detailed description of the difference between Func and Action, funcaction

Differences between Func and Action

I. Func

Func is A. Net built-in delegate.

Func <Result>, Func <T1, Result> is a. Net built-in generic delegate.

Func<TResult>Func<T,TResult>Func<T1,T2,TResult>Func<T1,T2,T3,TResult>Func<T1,T2,T3,T4,TResult>

It has five forms, but the number of parameters is different. The first is that there is no parameter, but there is a return value;

The following is an example of a simple normal delegate to transfer methods.

private delegate string Say();public static string SayHello(){  return "Hello";}static void Main(string[] args){  Say say = SayHello;  Console.WriteLine(say());  Console.ReadKey();}

So sometimes, when we don't know what operations an interface is doing at the same time, I can leave a delegate for it.

For convenience,. Net directly has a delegate by default. Let's try again. Net's default delegate.

public static string SayHello(){  return "Hello";}static void Main(string[] args){  Func<string> say = SayHello;  Console.WriteLine(say());  Console.ReadKey();}

If you need parameters, you can also upload them in this way.

Public static string SayHello (string str) {return str + str;} static void Main (string [] args) {Func <string, string> say = SayHello; string str = say ("abc"); Console. writeLine (str); // output abcabc Console. readKey ();}

Ii. Action

The usage of Action <T> is almost the same as that of Func, and the call method is similar.

ActionAction<T>Action<T1,T2>Action<T1,T2,T3>Action<T1,T2,T3,T4>

private delegate string Say();public static void SayHello(string str){  Console.WriteLine(str);}static void Main(string[] args){  Action<string> say = SayHello;  say("abc");  Console.ReadKey();}

Iii. Differences between Func and Action

Func works almost the same as Action. Just

Func <Result> has a return type;

Action <T> only the parameter type cannot be input. Therefore, the delegate functions of Action <T> do not return values.

4. Both Func AND Action support Lambda calls.

Return the repeated value after an input as an example.

Func <string, string> say = m => m + m; Console. WriteLine (say ("abc"); // output abcabc

5. Most Common Func scenarios

Generally, Func is most common in the method parameters as follows:

string XXX(Func<string, string>)

Let's take a look at one of the Sum in Linq:

public static int Sum<TSource>(this IEnumerable<TSource> source, Func<TSource, int> selector);

There are two points:

1. The extension method is irrelevant to this article (the extension is IEnumerable <TSource>, mainly to implement the set of IEnumerable <TSource> interfaces. Output Functions ).

2. Func <TSource, int> selector.

Try to write a function named first2. There are many exception handling and many design patterns in the source code of Linq. Unfortunately, I don't understand them, but I only extract simple logic.

Namespace ConsoleApplication2 {static class Extend {public static TSource First2 <TSource> (this IEnumerable <TSource> source, Func <TSource, bool> predicate ){//.. Net source code, exception handling, many design patterns, I don't understand, just extract the logic foreach (TSource item in source) {if (predicate (item )) {return (item) ;}} throw new Exception ("the first element that meets the condition does not exist! ") ;}} Class Program {static void Main (string [] args) {List <int> ListInt = new List <int> () {1, 2, 3, 4, 5}; int k = ListInt. first2 (m => m> 4); // output 5 Console. writeLine (k); Console. readKey ();}}}

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