What is the C# equivalent of the friend keyword in C++?

The core of designing immutable objects and data structures in C# is to ensure that the state of the object is not modified after creation, thereby improving thread safety and reducing bugs caused by state changes. 1. Use readonly fields and cooperate with constructor initialization to ensure that the fields are assigned only during construction, as shown in the Person class; 2. Encapsulate the collection type, use immutable collection interfaces such as ReadOnlyCollection or ImmutableList to prevent external modification of internal collections; 3. Use record to simplify the definition of immutable model, and generate read-only attributes and constructors by default, suitable for data modeling; 4. It is recommended to use System.Collections.Imm when creating immutable collection operations.

Common problems with async and await in C# include: 1. Incorrect use of .Result or .Wait() causes deadlock; 2. Ignoring ConfigureAwait(false) causes context dependencies; 3. Abuse of asyncvoid causes control missing; 4. Serial await affects concurrency performance. The correct way is: 1. The asynchronous method should be asynchronous all the way to avoid synchronization blocking; 2. The use of ConfigureAwait(false) in the class library is used to deviate from the context; 3. Only use asyncvoid in event processing; 4. Concurrent tasks need to be started first and then await to improve efficiency. Understanding the mechanism and standardizing the use of asynchronous code that avoids writing substantial blockage.

The correct way to use dependency injection in C# projects is as follows: 1. Understand the core idea of DI is to not create objects by yourself, but to receive dependencies through constructors to achieve loose coupling; 2. When registering services in ASP.NETCore, you need to clarify the life cycle: Transient, Scoped, Singleton, and choose according to business needs; 3. It is recommended to use constructor injection, and the framework will automatically parse dependencies, which are suitable for controllers and services; 4. Built-in containers can be used in small projects, and third-party containers such as Autofac can be introduced in complex scenarios, and custom service registration and configuration reading are supported. Mastering these key points can help improve the testability, maintainability and scalability of your code.

Key strategies for handling exceptions and error management include: 1. Use the try-catch block to catch exceptions, put the possible error code in try, specify the specific exception type in the catch to process, avoid empty catch blocks; 2. Do not overuse exceptions, avoid using exceptions to control normal logic, and give priority to using conditional judgment; 3. Record and pass exception information, use log library to record stack information, and retain original exceptions when retold; 4. Reasonably design custom exceptions to distinguish system exceptions and business errors, but should be used in moderation; these methods help build more robust and maintainable applications.

TosecureASP.NETCoreAPIs,implementauthenticationandauthorizationusingAddAuthentication()andAddAuthorization(),enforceauthorizationgloballyandattheroutelevelwith[Authorize],validateallinputsviaDataAnnotationsorFluentValidation,sanitizeoutputstopreventX

Five steps to deploy C# applications to the cloud environment: First, make sure to use .NETCore or .NET5 and configure the release files and dependencies; second, choose cloud service types such as AzureAppService or AWSElasticBeanstalk according to your needs; third, manage sensitive information through environment variables instead of configuration files; fourth, enable log monitoring tools such as ApplicationInsights or CloudWatch; fifth, check logs regularly and set up health check interfaces for maintenance.

To create your own C# custom properties, you first need to define a class inherited from System.Attribute, then add the constructor and attributes, specify the scope of application through AttributeUsage, and finally read and use them through reflection. For example, define the [CustomAuthor("John")] attribute to mark the code author, use the [CustomAuthor("Alice")] to modify the class or method when applying, and then obtain the attribute information at runtime through the Attribute.GetCustomAttribute method. Common uses include verification, serialization control, dependency injection, and

When using var, it should be determined based on whether the type is clear and whether the readability is affected. 1. When the type is clear on the right side of the assignment, such as varlist=newList(); can improve the code simplicity; 2. When the type is fuzzy or returns to object or interface type, var should be avoided, such as IEnumerableresult=SomeMethod(); to improve readability; 3. Use var reasonably in anonymous types and LINQ queries, such as receiving anonymous objects, but subsequent processing is recommended to encapsulate it as a specific type; 4. In team projects, coding style should be unified, and var should be used reasonably through .editorconfig or code review to avoid abuse and affect maintenance.