Part 100 Func delegate in c#

What is Func<T,TResult> in C#?

In simple terms,Func<T,TResult> is just generic delegate. Depending on the requirement,the type parameters(T and TResult) can be replaced with the corresponding(对应的) type arguments.

For example,Func<Employee,string> is a delegate that represents(代表) a function expecting(期待) Employee object as an input parameter and returns a string.

class Program
    {
        static void Main(string[] args)
        {
            List<Employee> employees = new List<Employee>() { 
                new Employee{ID=101,Name="lin1"},
                new Employee{ID=102,Name="lin2"},
                new Employee{ID=103,Name="lin3"}
            };

            //Func<Employee, string> selector = e => "name=" + e.Name;
            IEnumerable<string> employeeNames = employees.Select(e => "name=" + e.Name);
            foreach (string name in employeeNames)
            {
                Console.WriteLine(name);
            }

        }
    }
    class Employee
    {
        public int ID { get; set; }
        public string Name { get; set; }
    }

What is the difference between Func delegate and lambda expression?

They're the same, just two different ways to write the same thing. The lambda syntax is newer, more concise(简洁) and easy to write.

What if I have to pass two or more input parameters?

As of this recording there are 17 overloaded versions of Func, which enables us to pass variable number and type of input parameters. In the example below, Func<int,int,string> represents a function that expects 2 int input parameters and returns a string.

class Program
    {
        static void Main(string[] args)
        {           
            Func<int, int, string> funcDelegate = (num1, num2) => (num1 + num2).ToString();
            string result = funcDelegate(10,20);
            Console.WriteLine("sum="+result);

        }
    }

Finally, I completely learning the  C# language, go to bed, good night guy.