. NET-based custom generics

Generics are used very frequently in. NET, and in console applications, the default introduces the System.Collection.Generics namespace, which provides the generic:list<t> and dictionary<t that we often use Believe that they have been used to know their strength. There is also a simple generic type that we often use: system.nullable<t> We can:

 System.Nullable<int> Nullableint; declares a nullable int type, because C # syntax simplifies this usually we do not write this way, but write:  int? Nullableint The following highlights how to customize generics.     defining generic classes   creating generic classes is required in the class definition with angle brackets syntax:  class mygenericclass<t>{    ...} T can be an arbitrary identifier, as long as you follow the naming convention.     can be used to type the class member's return type, method parameter type, etc., such as:  copy code class MYGENERICCLASS&LT;T1, T2, t3>{    Private T1 t1object;     Public MyGenericClass (T1 item)     {        T1object = item;& nbsp  }     Public T1 t1object    {        get        {& nbsp           return t1object;       }   }} Copy the code Note If you cannot assume what type is provided. The following code cannot execute:  copy code class MYGENERICCLASS&LT;T1, T2, t3>{    private T1 t1object;     public MyGenericClass ()     {        t1object = new T1 ();   }} Copy the code because we don't know if T1 has a public default constructor.    defAult keyword   If we define a generic field, we want to initialize it in the constructor, but we don't know whether it's a reference type or a value type, then default is useful:  public MyGenericClass () {     T1object = default (T1);} If the value type is assigned a value of 0, the reference type is assigned the value NULL.     constraint types   When defining generics we can constrain the type, implemented by the WHERE keyword:  class mygenericclass<t1> where T: constraint1,constraint{    ...} Constraint defines a constraint, with multiple constraints separated by commas, if there are multiple types:  class mygenericclass<t1, t2> where t1:constraint1 where t2:constraint{     ...} Here are some available constraints                                          constraints                                                  ,         &NB Sp       Description                            &NB Sp     where t:struct                                   Use structural constraints, type T must be a value type                                  wher E t:calss                                       class constraint specified, type T must be reference type                        &N Bsp         where t:interface                                   Specify type T must be implemented as interface or implement Interface                                  where T:base-class             &NBS P                 The specified type T must be a base class or derive from the basic class              & nbsp   &NBSp              where t:new ()                 &NBS P                     specifying type T must have a default constructor     The following combination of knowledge to give an example: (PS do not see the code is actually very simple patience to see)   first define four classes Animal, Cow, chicken, and supercow  copy code #region Animal virtual base class has a Name property Feed method and a virtual method makeanoise   //Virtual base class has a Name property feed method and a virtual method makeanoise    Public abstract class animal& nbsp   {        protected string name;         public string name  &nbsp ;     {            get            {    &NBSP ;           return name;           }        &NBS P   set            {                name = value;         &NBSP;  }       }         public Animal ()         {            name = "The animal with no name";       }     &NBSP ;   Public Animal (string newName)         {            name = NewName;        }         public void Feed ()         {  &nbsp ;         Console.WriteLine ("{0} has been fed", name);       }         public abstract void Makeanoise ();   }    #endregion复制代码复制代码//cow Animal subclasses to implement virtual methods & nbsp   public class cow:animal    {        public Cow (string name):      &NB Sp     Base (name)         {       }        public Overr IDE void makeAnoise ()         {            Console.WriteLine ("{0} says ' Moo! '", name);        }   } Copy Code copy Code//chicken class, Animal subclass     public class chicken:animal  &N Bsp {        public Chicken (string name)            : Base (name)   &NBSP ;     {}        public override void Makeanoise ()         {    & nbsp       Console.WriteLine ("{0} says ' Cluck '", name);       }   } Copy code copy code//cow Subclass, have a way of fly    class supercow:cow    {        public Supercow (string name): Base (name)          {       }         public void F Ly ()         {            Console.WriteLine ("{0} is flying!", name); &nbsp ;   &NBSp  }         public override void Makeanoise ()         {    &NBS P       Console.WriteLine ("{0} says ' I am supercow! '", name);       }     After the copy code class is ready, we can start defining our generics with the:  copy code//inherited iterator interface, which makes it easy to use the foreach constraint with its type animal and its subclasses     public class farm< t>:ienumerable<t> where t:animal    {        private list<t> animals = new List<t> ();         public list<t> animals        {    & nbsp       get             {                Return animals;               }       }       //iterator &nbs P       Public ienumerator<t> GetEnumerator ()         {            return animals. GetEnumerator ();       }         IEnumerator Ienumerable.getenumerator () & nbsp       {            return animals. GetEnumerator ();       }        //execute all Animal makeanoise ()     & nbsp   public void makenoises ()         {            foreach (T animal in Animals)             {                animal. Makeanoise ();           }       }       //execute all ANI Mal's feed ()         public void feedtheanimals ()         {            foreach (T Animal in animals)             {                Animal. FeeD ();           }       }       //get COW&N in animals Bsp       Public farm<cow> getcows ()         {          &NBSP ; farm<cow> cowfarm = new farm<cow> ();            foreach (T Animal in animals) &NB Sp           {                if (animal is Cow)   &NBSP ;             {                    COWFARM.A Nimals. ADD (animal as Cow);               }           }&NB Sp           return cowfarm;       }   } Copy the code generic definition OK, let's write the code to call it:  Copy code class program    {        static void Main (string[] args)         {&NBsp           farm<animal> Farm = new farm<animal> ();          & nbsp Farm. Animals.add (New Cow ("Jack"));            Farm. Animals.add (New Chicken ("Vera"));            Farm. Animals.add (New Chicken ("Sally"));            Farm. Animals.add (New Supercow ("Kevin"));            Farm. Makenoises ();             farm<cow> dairyfarm = Farm. Getcows ();            dairyfarm.feedtheanimals ();           & nbsp foreach (Cow Cow in Dairyfarm)             {                if (cow is Supercow)                 {          &NB Sp         (cow as Supercow). Fly ();      &nbsp        }           }            Console. ReadKey ();       }   }

. NET-based custom generic