C # features

• Yield

It is usually used in the iterator to provide a value to the IEnumerable object or end the iteration.

For example:

yield return expression; yield break;

• Var

Defines variables of the implicit type.

var i = 5; var s = "Hello";

 

Note that the implicit type (Implicitly typed) is not a "dynamic type" and is determined by the compiler during compilation.

• Default

In addition to providing default conditions in the switch statement, default is also used as a keyword in generics. For example:

T temp = default(T);

Because we do not know whether the T type is a reference or a value type, it cannot be used to compare it with null (only the reference type is available) or a number (the value type can be compared with it. If the default keyword is used, null is returned for the reference type, and 0 is returned for the value type.

Global ::

Keyword global: Used to reference a global namespace.

class TestClass : global::TestApp { }

Volatile

This field can be modified by multiple threads simultaneously in multiple threads. For more examples about how to use volatile multithreading, refer to how to: create and terminate a thread.

Public volatile int I; // C # can use the extern modifier to declare external implementation methods. // It is often used in Interop services to use unmanaged code together with the DllImport attribute (static must be declared at the same time) // For example: [DllImport ("avifil32.dll")] private static extern voidAVIFileInit (); // C # Can reference an assembly with the same type name (multiple versions of the same control) at the same time. // use an external command line to specify the alias reference at this time. // For example: /r: GridV1 = grid. dll/r: GridV2 = grid1_dll // when using them in the program // you need to use the key extern to reference them: extern alias GridV1; extern alias GridV2; // GridV1 and GridV2 will be referenced and the global namespace will have additional space at the same level // use GridV1: Grid or GridV2: Grid to get different version Grid types. // Syntax ?? The null merge operator is used to define the default value of the reference type that can be null. // If the left operand is not null, the left operand is returned. Otherwise, the right operand is returned. Int y = x ?? -1; // It is also a null Operator: static int? GetNullableInt () {return null;} //... or int? X = null; where T: new () // we know that you can use the where keyword to restrict generic definitions. // For example, public class MyClass <T, U> where T: class where U: struct {} // At the same time, we can include the constructor constraints in the generic definition // new () the constraint tells the compiler that any type of parameter contains a non-parameter (default) constructor. Public class MyGenericClass <T> where T: IComparable, new () {T item = new T ();} // language features Nullable type when we want to describe a value type that may not exist // use nullable to replace the value type // use? Modifier to declare an nullable type // such as: int? A = 1; // C # The Nullable class and Nullable struct are supported to support the nullable type. // The Nullable struct contains two useful attributes, HasValue and Value, to determine and obtain whether the current type has another Value. // Curryization may be a bit unfamiliar with. NET friends. // wikipedia translates the name as "kerryization"-I personally don't like it, but currying is used in English. // Curry is an implementation technology of functional programming. // The general process is to convert the function that originally accepts multiple parameters into a function with only the first parameter, and then return the new function to accept the remaining parameters. // A bit of interface, in addition, there are relatively few Chinese documents about functional programming or curry. // functional programming and curry interpretation/all languages that can implement closures can achieve curry. // In C #2.0, it can be implemented through anonymous delegation. In 3.0, curry is relatively simple: static class Program {static Func <TArg1, Func <TArg2, TResult> Curry <TArg1, TArg2, TResult> (this Func <TArg1, TArg2, TResult> f) {return a1 => a2 => f (a1, a2 );} static voidMain () {Func <int, int, int> add = (x, y) => x + y; var curriedAdd = add. curry (); Console. writeLine (curriedAdd (13) (29) ;}// interested in implementing functional programming using C # // more Code implementations can be found in the MSDN Code. // The anonymous type can be used to encapsulate a set of read-only attributes into a single object without explicitly defining a type. // The type name is generated by the compiler and cannot be used at the source code level. // The type is also determined by the compiler's inference. // Usually used with the select clause of the LINQ query expression // initialize the object var productQuery = from prod in products select new {prod. color, prod. price}; // create a new object, foreach (var v in productQuery) {Console. writeLine ("Color = {0}, Price = {1}", v. color, v. price);} // Extension Method C #3.0 can expand the type of CLR // For example, you may need to obtain the number of words in an English string // you can write a method to process the string in the past // now you can add a method to calculate the number of words for the string type: namespace ExtensionMethods {public static class MyE Xtensions {public static int WordCount (this String str) {returnstr. Split (new char [] {'', '.', '? '}, StringSplitOptions. removeEmptyEntries ). length ;}}// use this to extend the WordCount Method to the CLR built-in type. // you can use it directly like a common method: using ExtensionMethods ;//... string s = "Hello Extension Methods"; int I = s. wordCount (); // For more information, see the MSDN or ScottGu blog. // Method and attribute List. ForEach () Array or List has a very practical ForEach method // you can directly input a method to operate on elements in the set. // For example, List <String> names = new List <String> (); names. add ("Bruce"); names. add ("Alfred"); names. forEach (Print); names. forEach (delegate (String name) {Console. writeLine (name) ;}); private static void Print (string s) {Console. writeLine (s) ;}// GetValueOrDefault for nullable type objects // in addition to the two common attributes Value and HasValue // You can also use the GetValueOrDefault method to obtain the current Value or default Value: float? MySingle = 12.34f; float? YourSingle =-1.0f; yourSingle = mySingle. GetValueOrDefault (-222.22f); // yourSingle = 12.34 mySingle = null; yourSingle = mySingle. GetValueOrDefault (); // yourSingle = 0