What are the implementation methods of dependency injection in PHP7.0?

PHP 7.0 is a popular programming language that provides many advanced technologies, among which dependency injection is one of them. Dependency injection is a programming pattern that enables the creation and initialization of objects by passing dependencies to them when they are created. In this article, we will explore how dependency injection is implemented in PHP 7.0.

Dependency injection (DI) is a programming technique that avoids tight coupling by injecting dependencies into objects. By using DI we can make our code more flexible and extensible as we can easily extend and modify the code by changing dependencies.

1. Constructor injection

Constructor injection is the most common implementation of dependency injection. This is accomplished by accepting dependencies in the object's constructor. Here is an example:

class A {
    private $B;

    public function __construct(B $B) {
        $this->B = $B;
    }
}

class B {}

$B = new B;
$A = new A($B);

In this example, we inject B's dependency by accepting B in A's constructor. This approach is very common because the constructor is called when the object is created, so we can inject dependencies here.

2. Property injection

Property injection is a way to implement dependency injection by setting properties after the object is created. This approach is less common than constructor injection, but can be more flexible in some situations. The following is an example:

class A {
    private $B;

    public function setB(B $B) {
        $this->B = $B;
    }
}

class B {}

$B = new B;
$A = new A;
$A->setB($B);

In this example, we inject B's dependencies through the setB method. The main benefit of this approach is that we can create the object first and then inject the dependencies at a later time. This is useful for those situations where delayed dependency injection is required.

3. Interface injection

Interface injection is a way to define injection methods through interfaces. This method is very flexible because we can define injection methods by implementing interfaces to implement different types of injection methods. The following is an example:

interface DIInterface {
    public function setB(B $B);
}

class A implements DIInterface {
    private $B;

    public function setB(B $B) {
        $this->B = $B;
    }
}

class B {}

$B = new B;
$A = new A;
$A->setB($B);

In this example, we define a DI interface, which defines the setB method to inject B's dependencies. By implementing this interface, we can define different injection methods to implement different types of dependency injection.

Summary

In PHP 7.0, dependency injection is a very powerful programming technology. Three different dependency injection implementation methods are listed above, including constructor injection, property injection and interface injection. Each method has its own advantages and disadvantages, and we can choose the most suitable method according to our needs. Using dependency injection, we can make our code more flexible and extensible, thus making our applications more robust and reliable.

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