System.Func

Added in .NET 3.5
The Func delegate is used for methods that accept one or more arguments and return a value.
An anonymous function is an inline statement or expression that can be used wherever a delegate type is expected.
A delegate with a specific signature can be declared using the Func type.
The last parameter of the Func delegate is the output parameter or result parameter.

System.Func<string, string> delegate_variable = delegate(string param1) 
{ return parameter.ToUpper(); } 

instead of

delegate string Delegate_Type(string x); 

Delegate_Type delegate_variable delegate(string param1) 
{ return parameter.ToUpper(); } 

Scalar Function Example

This transforms an array by applying a delegate to each element in the array.

public class GenericProperties 
{ 
   public delegate T MyTransformer(T myArgument); 

   public static void MyTransform(T[] values, MyTransformer transform) 
   { 
      for (int i=0; I < values.Length; i++) 
      { 
         values[i] = transform(values[i]); 
      } 
   } 
} 

static double Log(double t) { return Math.Log(t); } 

static void Main() 
{ 
   double[] arr = { 2.0, 4.0, 6.0 }; 
   GenericProperties<double>.MyTransform(arr, Square); 
   foreach (double d in arr) 
   { 
      System.Console.Write(d + ","); 
   } 

   GenericProperties<double>.MyTransform(arr, Log); 
   foreach (double d in arr) 
   { 
      System.Console.Write(d + ","); 
   } 
} 

This delegate takes multiple input parameters (T1, T2, etc) and one output parameter (TResult)
In .NET 3.5 the following signatures were available.

public delegate TResult System.Func<out TResult>(T arg); 
public delegate TResult System.Func<in T, out TResult>(T arg); 
public delegate TResult System.Func<in T1, T2, out TResult>(T arg); 
public delegate TResult System.Func<in T1, T2, T3, out TResult>(T arg); 
public delegate TResult System.Func<in T1, T2, T3, T4, out TResult>(T arg);