Three ways of dependency injection in php

Inversion of Control (IoC) is a design principle in object-oriented programming that can be used to reduce the coupling between computer codes. The most common method is called Dependency Injection (DI). Below we will introduce to you the three methods of dependency injection in PHP.

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##1. Constructor injection

Inject the dependent object into the dependent object through the parameters of the constructor, and inject it when initializing the object.

Advantages:

After the object initialization is completed, the usable object can be obtained.

Disadvantages:

　●When there are many objects that need to be injected, the constructor parameter list will be very long;

　●Not flexible enough. If there are multiple injection methods, and each method only needs to inject a few specified dependencies, then multiple overloaded constructors need to be provided, which is troublesome

2. Setter method injection

IoC Service Provider injects the dependent object into the dependent class by calling the setter function provided by the member variable.

Advantages:

Flexible. Required objects can be selectively injected.

Disadvantages:

After the dependent object is initialized, it cannot be used because the dependent object has not been injected yet.

3. Interface injection

The dependent class must implement the specified interface, and then implement a function in the interface, which is used for dependency injection. The parameter of this function is the object to be injected.

Advantages

In interface injection, the name of the interface and the name of the function are not important, as long as the parameters of the function are the type of the object to be injected.

Disadvantages

The intrusion is too strong and is not recommended.

PS: What is an intrusion line?

If class A wants to use a function provided by others, if in order to use this function, it needs to add additional code to its own class, this is intrusive.

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