1. C# 5 and 6 Tips and Tricks Telerik Academy Plus http://academy.telerik.com C# Tips and Tricks

2. 1. C# 6 – History and Important New Features 2. Syntactic Sugar and Language Features 3. Traps 4. Useful.NET Classes and Methods Demos: github.com/NikolayIT/CSharp-Tips-and-Tricks github.com/NikolayIT/CSharp-Tips-and-Tricks 2

3. https://github.com/NikolayIT/CSharp-6-New-Features

4. 4 C# 1.0 VS 2002.NET 1.0 Managed Code C# 2.0 VS 2005.NET 2.0 Generics Generics ReflectionReflection Anonymous Methods Partial Class Nullable Types C# 3.0 VS 2008.NET 3.5 Lambda Expression LINQLINQ Anonymous Types Extension Methods Implicit Type (var) C# 4.0 VS 2010.NET 4.0 dynamicdynamic Named Arguments Optional Parameters More COM Support C# 5.0 VS 2012.NET 4.5 Async / Await Caller Information C# 6.0 VS 2015.NET 4.6 A lot of new syntax features….NET Compiler Platform (Roslyn)

5.  You can add an initializer to an auto-property, just as you can to a field:  The initializer directly initializes the backing field  Just like field initializers, auto-property initializers cannot reference "this" 5 public class Person { public string FirstName { get; set; } = "Nikolay"; public string FirstName { get; set; } = "Nikolay"; public string LastName { get; set; } = "Kostov"; public string LastName { get; set; } = "Kostov";} this. k__BackingField = "Nikolay";

6.  Auto-properties can now be declared without a setter:  The backing field of a getter-only auto- property is implicitly declared as read-only:  It can be assigned to via property initializer  In future releases it will be possible to assign it in the declaring type’s constructor body public string FirstName { get; } = "Nikolay";.field private initonly string ' k__BackingField' 6

7.  Methods as well as user-defined operators and conversions can be given an expression body by use of the “lambda arrow”:  The effect is exactly the same as if the methods had had a block body with a single return statement  For void returning methods - expression following the arrow must be a statement 7 public object Clone() => new Point(this.X, this.Y); public static Complex operator +(Complex a, Complex b) => a.Add(b);

8.  Expression bodies can be used to write getter- only properties and indexers where the body of the getter is given by the expression body  Note that there is no get keyword  It is implied by the use of the expression body syntax 8 public Person this[string name] => this.Children.FirstOrDefault( x => x.Name.Contains(name)); this.Children.FirstOrDefault( x => x.Name.Contains(name)); public string Name => FirstName + " " + LastName;

9.  Occasionally you need to provide a string that names some program element  When throwing ArgumentNullException  When raising a PropertyChanged event  When selecting controller name in MVC  nameof() = Compiler checks, navigation, easy for renaming (refactoring) 9 if (x == null) throw new ArgumentNullException(nameof(x)); @Html.ActionLink("Sign up",nameof(UserController),"SignUp")

10.  Syntactic sugar used to construct strings  Template strings containing expressions  Creates a string by replacing the contained expressions with their ToString represenations  As a result strings are easier to read/understand  Curly brackets are escaped by two brackets 10 // C# 5 var str = string.Format( "Name = {0}, hours = {1:hh}", name, hours); "Name = {0}, hours = {1:hh}", name, hours); // C# 6 var str = $"Name = {name}, hours = {hours:hh}"; Console.WriteLine($"{{name}}"); // Prints {name}

11.  The null-coalescing operator (??) returns:  The left-hand operand if the operand is not null  Otherwise it returns the right hand operand  Write:  Instead of:  It also can be chained: 11 var pageTitle = (title != null) ? title : "Default Title"; var pageTitle = title ?? "Default Title"; return firstValue ?? secondValue ?? thirdValue;

12.  Lets you access members and elements only when the receiver is not-null  Providing a null result otherwise  Can be used together with the null coalescing operator ??:  Can also be chained 12 int? length = customers?.Length; //null if customers is null Customer first = customers?[0]; //null if customers is null PropertyChanged?.Invoke(e) //PropertyChanged is an event int length = customers?.Length ?? 0; // 0 if customers null int? first = customers?[0].Orders?.Count();

14.  A generic type parameter can be one of:  Invariant (default) – meaning the generic type parameter cannot be changed  Contravariant – the generic type parameter can change from a class to a class derived from it  In C# we indicate this with the in keyword  Can appear only in input positions (method’s argument)  Covariant – the generic type argument can change from a class to one of its base classes  In C# we indicate this with the out keyword  Can appear only in output positions (method’s return type) 14

15.  ?: - ternary operator + chaining  Partials classes and methods?  Short initializing of arrays = { 1, 2, 3 }  extern alias for resolving namespace conflicts  params for arbitrary number of parameters  Custom Indexers public string this[string ind]  Omit generic type when call method X (y)  Multicast delegates (+=, -=) + Equality of delegates  @keyword for variable and class naming  public static explicit operator MyEntity  Hide Interface Implementation 15

17.  System.Object is the base class for all types  System.ValueType is the base class for all value types (struct & enum) 17

18.  All structs derive from the same ValueType class  The ValueType.Equals(Object) method overrides Object.Equals(Object) and provides the default implementation of value equality  By default when comparing structs with Equals()  If none of the fields of the current instance are reference types => byte-by-byte comparison  Otherwise it uses reflection to compare the corresponding fields (~20 times slower!)  We can improve the performance of structs by comparing them with overridden Equals 18

19.  Calling virtual methods in a constructor is a bad idea  When initializing a type in C# constructors are invoked top-down  First the top base constructor  Then down to the derived constructors through the inheritance  But virtual methods are invoked bottom-up  First the most derived overridden method  Then up to all base virtual methods  For this reason, if you call virtual methods in constructor you may have unexpected behavior from your classes 19

20.  Hash code is used in various hash-based collections (HashSet, Dictionary )  In C# an overridden method named GetHashCode provides the hash code generation for a particular type  If you generate custom hash code for a type, try to use read-only properties for it  Non-read-only properties may change the hash code run-time and collections will not be notified for the change  Thus the internal structure and algorithms of the collection will not be able to retrieve and use the modified instance 20

21.  The.NET runtime employs a very smart garbage collector to clean up objects that are no longer used  This doesn't mean that you'll never lose track of memory  Not removing event listeners  Any event listener that is created with an anonymous method or lambda expression that references an outside object will keep those objects alive  Keeping database connections or result sets open when they are not used  Call to functions using P/Invoke which allocate memory which you then never release 21

23.  The System.IO.FileSystemWatcher class makes it possible to execute code when certain files or directories are created, modified, or deleted  It listens to the file system change notifications and raises events  Few things to consider:  Sometimes events may be raised multiple times  Instance members are not thread safe  The watcher will continue listening until the EnableRaisingEvents is set to False  More: http://weblogs.asp.net/ashben/31773 http://weblogs.asp.net/ashben/31773 23

24.  Concat() – concatenates sequences  Order of which sequence comes first matters  Union() – c  Union() – c oncatenate sequences without duplicates  Duplicates are determined by using an IEqualityComparer or Equals() + GetHashCode() 24 PrintList(firstList.Concat(secondList)); // apples,bananas,cherries,durian,durian,eggplant,apples PrintList(firstList.Union(secondList)); // apples, bananas, cherries, durian, eggplant PrintList(firstList.Union(secondList,new LengthComparer())); // apples, bananas, cherries firstList = { "apples", "bananas", "cherries", "durian" }; secondList = { "durian", "eggplant", "apples" }

25.  Intersect() – subset of each collection that is found in both collections (i.e. common elements)  Except() – subtracts elements from a collection (i.e. first collection minus second one)  Both Intersect() and Except() depend on Equals() + GetHashCode() or IEqualityComparer  Both Intersect() and Except() depend on Equals() + GetHashCode() or IEqualityComparer 25 PrintList(firstList.Intersect(secondList)); // apples, durian PrintList(firstList.Except(secondList)); // bananas, cherries firstList = { "apples", "bananas", "cherries", "durian" }; secondList = { "durian", "eggplant", "apples" }

26.  Zip() – for each elements: combines element from the first sequence an with element from the second sequence using result selector function  Aggregate() – Applies an accumulator function over a sequence  Built-in: Count, Min, Max, Sum and Average 26 PrintList(listOfNumbers.Zip(firstList, Tuple.Create)); // (1, apples), (2, bananas), (3, cherries), (4, durian) Console.WriteLine(firstList.Aggregate((s, c) => s + c))); // applesbananascherriesdurian listOfNumbers = Enumerable.Range(1, 4); firstList = { "apples", "bananas", "cherries", "durian" };

27.  string.IsNullOrEmpty / IsNullOrWhiteSpace  Convert.ChangeType()  DateTime.ToLocalTime()  Char.GetUnicodeCategory()  Object.ReferenceEquals()  10.ToString("(+)#.##;(-)#.##;(nothing)")  Process.Start()  Array.AsReadOnly()  Array.Resize()  Array.CopyTo()  int.Parse("(24)",NumberStyles.Allow…)  DateTime.ParseExact()  BitConverter.GetBytes()  Custom format provider (IFormatProvider) 27

28.  Path.Combine() / Path.ChangeExtension()…  Configuration files  new Lazy () -> lazy initialization  char.GetNumericValue( ⅔ ) = 0.6666…  ZipFile.CreateFromDirectory  GZipStream / DeflateStream  Uri/UriBuilder class (relative, absolute, parts)  Task.Delay()  Joins  Debugging  [DebuggerStepThrough] + Just My Code  [DebuggerTypeProxy(typeof(SomeTypeProxy))] 28

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