(1) C# language feature that you need to know

(1) Lambda Expression

 

      (param1, param2, param3, ...) =>

     {

          statement1;

          statement2;

          statement3;

          ...

          return(lambda_expression_return_type);

     }

 

One simple demo:

    a) x => x

    b) This means input x, output x

 

One a little more complex demo:

(x, y) =>{ if( x > y ) { return (x); } else { return (y); }}

 

Note: delegate defines the input type and the return type, so please make sure your lambda expression meets your definition of delegate.

 

Another Demo:

class LambdaExpressionDemo { public delegate bool IntFilter<T>(T i); /// <summary> /// Filters a particular array. /// </summary> /// <typeparam name="T">Represents the type of the array.</typeparam> /// <param name="elements">The source array.</param> /// <param name="filter">The filter method.</param> /// <returns>The filtered array.</returns> public static T[] FilterArrayOfInts<T>(T[] elements, IntFilter<T> filter) { List<T> aList = new List<T>(); foreach (T i in elements) { if (filter(i)) { aList.Add(i); } } return (T[])(aList.ToArray()); } }

 

Below code is a simple lambda call for above code:

class Program { static void Main(string[] args) { #region ------- (1) Lambda Expression Demonstration ------- int[] source = { 3, 2, 7, 5, 3, 8 }; int[] ints = LambdaExpressionDemo.FilterArrayOfInts<int>(source, i => (i & 1) !=0); foreach (int oneInt in ints) { Console.WriteLine(oneInt); } #endregion } }

(2) Expression Tree

 

a) Definition

It's a very useful and valuable expression of data, it's a lambda exression that displaying the query operator by using the methodology of tree.

 

b) Simple Demo

     string[] names = { "Lucas Luo", "Bill Gates", "Steve Jobs", "Micheal Jackson" }; IEnumerable<string> lengthOfNameGreaterThan9 = names .Where(i => i.Length > 9) .OrderBy(i => i);

 

(3) Keyword "var", "object initialization" and "anonymous type"

 

a) They are all strongly connected. This means that we can hardly understand the "var" keyword without introducing the concept of "Object Initialization" and "Anonymous Type".

 

b) Simple Demo:

var anonymousType = new { Name = "Lucas Luo", Career = "Software Engineer"};

 

c) "var" keyword: it can conclude the data type by determining the initialized data type.

d) Failed by only using the declaration:

   

 var myVarType;

 

Error Message:

         Error 1 Implicitly-typed local variables must be initialized C:/Users/Lucas/documents/visual studio 2010/Projects/LinqToObjectViaCSharp/LinqToObjectViaCSharp/Program.cs 36 17 LinqToObjectViaCSharp

Explaination:

         The implicityly-typed local variables are all used static detection during complie period, so that the initialization program is needed to use. Otherwise it cannot conclude the type of this data type.

 

Another Error is coming by using below code:

var myStringType = "Lucas Luo";myStringType = 1;Console.WriteLine(name);------------------------------------------------------------------------- Error Message ------------------------------- Error1Cannot implicitly convert type 'int' to 'string'C:/Users/Lucas/documents/visual studio 2010/Projects/LinqToObjectViaCSharp/LinqToObjectViaCSharp/Program.cs3728LinqToObjectViaCSharp--------------------------------------------------------------------------------------------------------------------------

 

e) Initialization expression of Object and Agregator

    By typing a space to invoke the intellisense.

using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace ConsoleApplication1{ class Person { public string Name { get; set; } public int Age { get; set; } public string Career { get; set; } } class Program { static void Main(string[] args) { Person p = new Person { Name = "Lucas Luo", Age = 26, Career = "Software Engineer" }; } }}

 

(f) Agregator Initialization:

List<int> ints = new List<int> { 1, 3, 5, 4, 2, 19 };List<string> countries = new List<string> { "China", "USA", "Japan" };

 

g) Extension Method

Definition: It's a static method that used in a static class.

 

( Continue tomorrow... )