----------
20210306

Func.txt 

Func vs Action

摘要:
Action 等於 (沒有回傳值的delegate, 或 void foo()...)
Action                   等於 public delegate void Action();
Action<T>                等於 public delegate void Action<in T>(T obj);
Action<T1>               等於 public delegate void Action<in T1, in T2>(T1 arg1, T2 arg2);
Action<T1, T2>           以下依此類推
Action<T1, T2, T3>
Action<T1, T2, T3, T4>

Func<TResult> 等於 (回傳值型別為 TResult 的 delegate)
  Func 一定有回傳值 <TResult>, 因此沒有這種函數 "Func", 不像"Action"可以沒有回傳值.
Func<TResult>              等於 public delegate TResult Func<out TResult>();
Func<T, TResult>           等於 public delegate TResult Func<in T, out TResult>(T arg);
Func<T1, T2, TResult>      等於 public delegate TResult Func<in T1, in T2, out TResult>(T1 arg1, T2 arg2); 
Func<T1, T2, T3, TResult>  以下依此類推
Func<T1, T2, T3, T4, TResult>
Func<T1, T2, T3, T4, T5, TResult>


----------
20181120

放到arg方式的samples:
        public static string GetTaskResultString(Func<string> funcReturnString)
        {
            return Task.Run<string>(funcReturnString).Result;
        }
        public static string GetTaskResultStringWithArgString(Func<object, string> funcReturnStringInObject, object oData)
        {
            return Task.Factory.StartNew<string>(funcReturnStringInObject, oData).Result;
        }
		
		sample2:
        public override Dictionary<Func<bool>, string> GetParamExceptionDictionary()
        {
            Dictionary<Func<bool>, string> _exceptionChecks = new Dictionary<Func<bool>, string>();

			// lambda 方式建立Func<bool>函數
            Func<bool> _isDateInFuture = new Func<bool>(() => DateTime.Now <= this.DOB);

            _exceptionChecks.Add(_isDateInFuture, "Please choose a date of birth that is not in the future!");
            return _exceptionChecks;
        }	
        private void PostInitialize()
        {
            if (GetHelpIfNeeded() == string.Empty)
            {
                SwitchParser.ParseSwitches(args);
            }
            _paramExceptionDictionary = new Dictionary<Func<bool>, string>();
            AddAdditionalParamChecks();
			// 取用Func<bool>函數
            foreach (var item in GetParamExceptionDictionary()) _paramExceptionDictionary.Add(item.Key, item.Value);
        }

		

呼叫方式:		
	    Console.WriteLine(ZTask.GetTaskResultString(myFuncString1));
        Console.WriteLine(ZTask.GetTaskResultStringWithArgString(myFuncString2, "with data"));	
        string myFuncString1()
        {
            return ($"myFuncString1(), {ZThreading.GetCurrentManagedThreadID()}");
        }
        string myFuncString2(object o1)
        {
            return ($"myFuncString2(), o1={o1.ToString()}, {ZThreading.GetCurrentManagedThreadID()}");
        }
		

----------
20181120

ref:
https://docs.microsoft.com/en-us/dotnet/api/system.func-2?redirectedfrom=MSDN&view=netframework-4.7.2

using System;
public class Anonymous
{
   public static void Main()
   {
      Func<string, string> convert = delegate(string s)
         { return s.ToUpper();}; 
         
      string name = "Dakota";
      Console.WriteLine(convert(name));   
   }
}

You can also assign a lambda expression to a Func<T,TResult> delegate, as the following example illustrates. (For an introduction to lambda expressions, see Lambda Expressions and Lambda Expressions.) 
// 上面的範例可改寫為以下 lambda 運算式:

using System;
public class LambdaExpression
{
   public static void Main()
   {
      Func<string, string> convert = s => s.ToUpper();
         
      string name = "Dakota";
      Console.WriteLine(convert(name));   
   }
}



----------
20181112

Action 等於 (沒有回傳值的delegate, 或 void foo()...)
Func   等於 (有回傳值的delegate)


Action 等於 (沒有回傳值的delegate, 或 void foo()...)
Action                   等於 public delegate void Action();
Action<T>                等於 public delegate void Action<in T>(T obj);
Action<T1>               等於 public delegate void Action<in T1, in T2>(T1 arg1, T2 arg2);
Action<T1, T2>           以下依此類推
Action<T1, T2, T3>
Action<T1, T2, T3, T4>

Func   等於 (有回傳值的delegate)
Func<TResult>              等於 public delegate TResult Func<out TResult>();
Func<T, TResult>           等於 public delegate TResult Func<in T, out TResult>(T arg);
Func<T1, T2, TResult>      等於 public delegate TResult Func<in T1, in T2, out TResult>(T1 arg1, T2 arg2); 
Func<T1, T2, T3, TResult>  以下依此類推
Func<T1, T2, T3, T4, TResult>
Func<T1, T2, T3, T4, T5, TResult>

  .net 語法如下: public delegate void Action();
如果需要(沒有參數 且 有回傳值的delegate), 則可以generic Func<TResult> delegate建立。
  Action<T1,T2...Tn>

Encapsulates a method that has no parameters and does not return a value.

You can use this delegate to pass a method as a parameter without explicitly declaring a custom delegate. The encapsulated method must correspond to the method signature that is defined by this delegate. This means that the encapsulated method must have no parameters and no return value. (In C#, the method must return void. In Visual Basic, it must be defined by the Sub…End Sub construct. It can also be a method that returns a value that is ignored.) Typically, such a method is used to perform an operation.


----------
sample1:

When you use the Action delegate, you do not have to explicitly define a delegate that encapsulates a parameterless procedure. For example, the following code explicitly declares a delegate named ShowValue and assigns a reference to the Name.DisplayToWindow instance method to its delegate instance.

using System;
using System.Windows.Forms;

public delegate void ShowValue();

public class Name
{
   private string instanceName;

   public Name(string name)
   {
      this.instanceName = name;
   }

   public void DisplayToConsole()
   {
      Console.WriteLine(this.instanceName);
   }

   public void DisplayToWindow()
   {
      MessageBox.Show(this.instanceName);
   }
}

public class testTestDelegate
{
   public static void Main()
   {
      Name testName = new Name("Koani");
      ShowValue showMethod = testName.DisplayToWindow;
      showMethod();
   }
}

----------
sample2:

The following example simplifies this code by instantiating the Action delegate instead of explicitly defining a new delegate and assigning a named method to it

using System;
using System.Windows.Forms;

public class Name
{
   private string instanceName;

   public Name(string name)
   {
      this.instanceName = name;
   }

   public void DisplayToConsole()
   {
      Console.WriteLine(this.instanceName);
   }

   public void DisplayToWindow()
   {
      MessageBox.Show(this.instanceName);
   }
}

public class testTestDelegate
{
   public static void Main()
   {
      Name testName = new Name("Koani");
      Action showMethod = testName.DisplayToWindow;
      showMethod();
   }
}


----------
sample3:
You can also use the Action delegate with anonymous methods in C#, as the following example illustrates. (For an introduction to anonymous methods, see Anonymous Methods (C# Programming Guide).)

using System;
using System.Windows.Forms;

public class Name
{
   private string instanceName;

   public Name(string name)
   {
      this.instanceName = name;
   }

   public void DisplayToConsole()
   {
      Console.WriteLine(this.instanceName);
   }

   public void DisplayToWindow()
   {
      MessageBox.Show(this.instanceName);
   }
}

public class Anonymous
{
   public static void Main()
   {
      Name testName = new Name("Koani");
      Action showMethod = delegate() { testName.DisplayToWindow();} ;
      showMethod();
   }
}


----------
sample4:

You can also assign a lambda expression to an Action delegate instance, as the following example illustrates. (For an introduction to lambda expressions, see Lambda Expressions (C# Programming Guide).)

using System;
using System.Windows.Forms;

public class Name
{
   private string instanceName;

   public Name(string name)
   {
      this.instanceName = name;
   }

   public void DisplayToConsole()
   {
      Console.WriteLine(this.instanceName);
   }

   public void DisplayToWindow()
   {
      MessageBox.Show(this.instanceName);
   }
}

public class LambdaExpression
{
   public static void Main()
   {
      Name testName = new Name("Koani");
      Action showMethod = () => testName.DisplayToWindow();
      showMethod();
   }
}

-----------
Action 參數

        // If you know what parameter you want to pass, take a Action<T> for the type. Example:
        // 若已知要傳入的參數型態, 則可明確宣告型態傳入, 如下例的<int>
        void LoopMethod(Action<int> code, int count)
        {
            for (int i = 0; i < count; i++)
            {
                code(i);
            }
        }

        // If you want the parameter to be passed to your method, make the method generic:
        // 若也需要傳入參數型態, 則可將函數改為generic方式.
        void LoopMethod<T>(Action<T> code, int count, T paramater)
        {
            for (int i = 0; i < count; i++)
            {
                code(paramater);
            }
        }