The key to achieving loose coupling is to reduce direct dependence between modules and improve the maintainability, scalability and testability of the system. 1. Use interfaces or abstract classes to define dependencies, so that the caller only relies on abstraction rather than concrete implementations, so that the implementation is replaced without affecting the calling logic; 2. Introduce event-driven or message mechanisms to enable modules to communicate through events or messages, reducing synchronous dependencies; 3. Control the direction of dependency and follow the principle of dependency inversion. Both high-level and low-level modules rely on abstraction to maintain the stability of core logic; 4. Reasonably divide the boundaries of modules, divide modules according to business capabilities, avoid confusion of responsibilities, and ensure independent changes of modules.

To achieve loose coupling, the key is to make the individual modules or components in the system directly depend on each other as little as possible. This not only improves the maintainability of the code, but also improves the scalability and testability of the system. Let’s take a look at how to do this from a few practical perspectives.

1. Define dependencies using interfaces or abstract classes

In object-oriented programming, defining the interaction between modules through interfaces or abstract classes is the basis for achieving loose coupling. The advantage of this is that the caller only relies on abstraction and does not care about concrete implementations.

• Example : For example, in a payment system, you define a PaymentProcessor interface instead of using WechatPayService or AlipayService directly. In this way, when you want to change the payment channel, you only need to replace the specific implementation without changing the calling logic.
• suggestion :
  • Try to avoid directly new low-level objects in high-level modules
  • The idea of ??using more than one "interface-oriented programming"
  • Better use with dependency injection (DI)

2. Introduce event-driven or message mechanism

When there is no need for strong synchronous calls between two modules, you can consider using events or message queues for communication. This method can make the sender and the receiver unaware of each other, further reducing the coupling degree.

• For example, if a user needs to send emails, record logs and other operations after registering, you can use the "User Registration Successful" event to notify other modules of processing, rather than calling methods one by one.
• You can use message middleware like Kafka and RabbitMQ, or use the event bus mechanism that comes with the language.

This approach is particularly suitable for cross-service communication, or collaboration between multiple subsystems.

3. Control the direction of dependency: the principle of inversion of dependency

The Dependency Inversion Principle (DIP) is one of the SOLID principles, which means "high-level modules should not rely on low-level modules, both should rely on their abstraction."

For example, business logic should not directly call specific classes accessed by databases, but rather go through a data access interface. In this way, even if the underlying storage method changes (such as changing from MySQL to MongoDB), the upper logic almost does not need to be changed.

• Practical skills:
  • Extract core business logic into independent modules
  • All external dependencies are exposed through the interface
  • Use containers to manage dependencies (such as Spring, Autofac)

4. Rationally divide module boundaries

The premise of loose coupling is that the module division is reasonable. If the module responsibilities are chaotic, even if the interface is used, it may be broken.

• How to determine whether the module is reasonable?

  • A module should have only one reason to change
  • If modifying a function causes multiple modules to be modified, it means there is a problem with the boundary

• Suggested practices:

  • Dividing modules according to business capabilities (rather than technical levels)
  • Use Domain Driven Design (DDD) to help identify boundaries
  • Avoid "God Class" or "Universal Service"

Basically these are the methods. Although they all seem to be cliché design principles, they are easily overlooked in actual development. Especially when the project is rushing to progress, many people will write tightly coupled code directly for the sake of convenience, and the maintenance will be particularly painful later. Loose coupling is not achieved overnight, but as long as you spend more time designing, it will save a lot of trouble in the long run.

The above is the detailed content of How to achieve loose coupling?. For more information, please follow other related articles on the PHP Chinese website!