Detailed func<t> and action<t> difference _ practical skills

The difference between func<t> and action<t> is explained

First, Func

Func is a. NET built in delegate.

Func<result>,func<t1,result> is a. NET-built generic delegate.

func<tresult>
func<t,tresult>
func<t1,t2,tresult>
func<t1,t2,t3,tresult>
func<t1,t2,t3,t4,tresult>

It has 5 forms, but the number of parameters is different; the first one is without parameters, but there is a return value;

The following is an example of a simple generic delegate to pass a method.

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 an interface is going to do at the same time, I can leave it a delegate.

In order to be more convenient,. NET has a delegate directly by default. Let's try again. NET Default-band 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 pass a copy.

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 ();
}

Second, Action

The use of action<t> is almost the same as Func, and the calling method is similar.

Action
action<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. the difference between Func and action

Func is almost the same as action. It's just that

Func<result> has return type;

Action<t> only the parameter type and cannot pass the return type. So action<t> 's delegate function has no return value.

Four, Func and action support the form of a lambda call

Or, after one input, return the duplicate value as an example.

Func<string, string> say = m => m + m;
Console.WriteLine (Say ("abc")); Output ABCABC

V. The most common places to Func

Usually the most common to Func is in the parameters of the method 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);

Inside see two points:

1, extension method, and this article is irrelevant (extended is ienumerable<tsource>, mainly to be able to implement the Ienumerable<tsource> interface of the collection.).

2, Func<tsource, int> selector this parameter.

Try to write a LINQ, named First2. LINQ source code has a lot of exception handling, many design patterns, unfortunately I do not understand, only the extraction of simple logic.

Namespace ConsoleApplication2
{
  static class Extend
  {public
    static TSource first2<tsource> ( This ienumerable<tsource> source, Func<tsource, bool> predicate)
    {
      //. NET own source code a lot of unusual situation processing, many design pattern, I also do not understand, only extracts the logic
      foreach (TSource item in Source)
      {
        if (predicate (item))
        { return
          (item);
        }
      throw new Exception ("No first element satisfies the condition!") ");
    }
  }
  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 ();}}

The above is the entire content of this article, there are problems can be linked with small, thank you for the support of the cloud-Habitat community!