© Copyright SELA software & Education Labs Ltd Baruch Hirsch St.Bnei Brak Israel 1 בס " ד

2 Dynamic lookup Named and optional parameters COM-specific interop features Variance

3 Dynamic objects are declared using the “dynamic” keyword When declaring a type as Dynamic there is no design time type checking And certainly no IntelliSence … Missing properties or methods will cause an exception at run time Calling a method on a dynamic object will always return a dynamic object The object can be a.NET object, a COM object, or even an html object

4 dynamic id = ; dynamic name = "Miki Mouse"; dynamic students = new List () { "yossi", "dana", “noam" }; Console.WriteLine(++age); students.Add("shara"); foreach (dynamic item in students ) { Console.WriteLine(item); }

5 The dynamic keyword is NOT like the var keyword var is resolved as design time dynamic is only resolved at runtime var x = 10; x = "name"; dynamic y = 10; y = "name";

6 public static int Sum(params int[] values) { int sum = 0; for (int i = 0; i < values.Length; i++) { sum += values[i]; } return sum; } public static double Sum(params double[] values) { double sum = 0; for (int i = 0; i < values.Length; i++) { sum += values[i]; } return sum; }

7 public static dynamic Sum(params dynamic[] values) { dynamic sum = values[0]; for (int i = 1; i < values.Length; i++) { sum += values[i]; } return sum; } Console.WriteLine(Sum(2, 3, 4)); Console.WriteLine(Sum("a", "b", "c")); Console.WriteLine(Sum(DateTime.Now, new TimeSpan(3, 3, 3)));

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9 Python Binder Ruby Binder COM Binder JavaScript Binder Object Binder Dynamic Language Runtime Expression Trees Dynamic Dispatch Call Site Caching IronPythonIronPythonIronRubyIronRubyC#C#VB.NETVB.NETOthers…Others…

10 static void Main(string[] args) { int i = 10; object o = new object(); dynamic i1 = i; dynamic o1 = o; }

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14 namespace Microsoft.CSharp.RuntimeBinder { public class CSharpSetMemberBinder { } namespace ProxyBinder { public class ProxyCSharpSetMemberBinder : CSharpSetMemberBinder { } } namespace Microsoft.CSharp.RuntimeBinder { public class CSharpSetMemberBinder : ProxyCSharpSetMemberBinder { } }

15 Access to members is limited by Accessibility level (no access to private members) No access to static members or extension methods

16 public static class Math { public static decimal Abs(decimal value); public static double Abs(double value); public static float Abs(float value); public static int Abs(int value); public static long Abs(long value); public static sbyte Abs(sbyte value); public static short Abs(short value); } public class Persons { public void Add(string name, int id, float age); public void Add(string name, int id); public void Add(string name); }

17 Default value can be a Constant, null or default Ctor of Struct Must (officially) appear after all required parameters static void Add(int id, string name = "", float age = 0) { }

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19 static void Add(int id, string name = "", float age = 0) {} static void Add(int id, [Optional, DefaultParameterValue("")] string name, [Optional, DefaultParameterValue(0)] float age) {} static void Add(DateTime dt1 = new DateTime(), DateTime dt2 = default(DateTime)) {} static void Add([Optional]DateTime dt1, [Optional]DateTime td2) {}

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21 static void Main(string[] args) { Add(); } static void Add(string name = "shlomo") { }

22 static void Main(string[] args) { Add("shlomo"); } static void Add( [Optional, DefaultParameterValue("shlomo")] string name) { }

23 static void Add(int id, string name = "shlomo", float age = 0) { } static void Main() { Add(22,, 24); } static void Main() { Add(22, age: 24); }

24 Advantages: – Named parameters can be used even for non-optional parameters – It can makes the method call clearer Disadvantages: – You cannot change the names of parameters in public methods – The order of sent parameters can change the result

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26 Covariance: delegate object CovarianceDelegate(); static Person CovarianceMethod(){ } CovarianceDelegate cd = CovarianceMethod; Contravariance: delegate void ContravarianceDelegate(Person obj); static void ContravarianceMethod(object obj) ContravarianceDelegate cva = ContravarianceMethod;

27 void PrintAllItems(List list) { foreach (var item in list) { Console.WriteLine(item); } void f() { List list = new List () { "name", "abcde", "1234" }; PrintAllItems(list); } void PrintAllItems(IEnumerable list)

28 class Person : IComparer { public int Compare(Person x, Person y) { } } class Employee : Person { } IComparer comparer = new Person();

29 static Action GetAction() { } Action action = GetAction();

30 public interface IEnumerable : IEnumerable { IEnumerator GetEnumerator(); } public interface IComparer { int Compare(T x, T y); } public delegate void Action (T obj);

31 My Blog (in Hebrew) C# 4.0 Post Collection 2/c-4-0-table-of-content.aspx PDC 2008 : Future of C# session.

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