The PHP Macro package offers closure (anonymous function) based setter dependency injection by providing a trait which can be included into any class.

composer req aimeos/macro

This package is for application, framework and library developers who want to allow customizing the behavior of their code by their users.

In applications, frameworks or libraries which are build for customization it’s necessary to allow overwriting existing functionality to be able customize its behavior. This is where macros are very handy because they can add custom code using closures.

With the PHP Macro package, you can also allow users to overwrite methods in base classes without forcing your users to extend these classes. The PHP Macro package uses NO reflection or other hacks, just pure PHP methods.

There are some pros and cons when compared to class based depencency injection:

Pro:

• Less code to write and much easier to implement for simple stuff
• Custom closures can be inherited and overwritten like class methods

Con:

• Limited static code analysis possibilities
• Anonymous function can not be forced to implement an interface

Thus, it's not a replacement for class based depencency injection but a lightweight addition for small extension points where full-blown dependency injection using classes implementing interfaces are too much work.

The result of existing methods can be modified if the original method checks for an existing macro and use that instead its own implementation:

// original code

class Order
{
    use Aimeos\Macro\Macroable;

    private $id = '123';

    public function getOrderNumber()
    {
        $fcn = static::macro( 'orderNumber' );
        return $fcn ? $fcn( $this->id ) : $this->id;
    }
};

Now, you can add your custom orderNumber macro that will be used instead:

// user code

Order::macro( 'orderNumber', function( string $id ) {
   return date( 'Y' ) . '-' . $id;
} );

(new Order)->getOrderNumber(); // now returns '2020-123'

Thus, you can generate own output or pass a different result to subseqent methods within the application.

When macros are called in an object context, they can also access class properties:

// original code

class A
{
    use Aimeos\Macro\Macroable;
    private $name = 'A';
};

Here, the private property $name is available in the macro:

// user code

A::macro( 'concat', function( array $values ) {
   return $this->name . ':' . implode( '-', $values );
} );

(new A)->concat( ['1', '2', '3'] ); // returns 'A:1-2-3'

The macro can use the property as input for creating the returned value.

The PHP macro package also allows to inherit macros from parent classes. Then, they can access class properties of the child class just like regular class methods:

// original code

class A
{
    use Aimeos\Macro\Macroable;
    private $name = 'A';
};

class B extends A
{
    private $name = 'B';
};

Macros added to the parent class will be available in child classes too:

// user code

A::macro( 'concat', function( array $values ) {
   return $this->name . ':' . implode( '-', $values );
} );

(new B)->concat( ['1', '2', '3'] ); // returns 'B:1-2-3'

Class B extends from class A but provides a different $name property. The macro inherited from class A will now use the property of class B.

It's also possible to overwrite macros inherited from parent classes as it's possible with regular class methods:

// original code

class A
{
    use Aimeos\Macro\Macroable;

    public function do() {
        return static::macro( 'concat' )( [1, 2, 3] );
    }
};

class B extends A {};

class C extends A {};

Now you can add macros to the parent class and one of the child classes:

// user code

A::macro( 'concat', function( array $values ) {
   return implode( ',', $values );
} );

C::macro( 'concat', function( array $values ) {
   return implode( '-', $values );
} );

(new B)->do(); // returns '1,2,3'

(new C)->do(); // returns '1-2-3'

This enables you to add special handling for single classes even if all other classes still use the macro added to class A.

Base classes often offer a set of methods that are used by the child classes. In PHP, replacing the methods of a base class is impossible and thus, you have to overwrite each child class with your own implementation.

To avoid that, the original method can use the call() method instead of calling the method of the parent class directly:

// original code

class A
{
    use Aimeos\Macro\Macroable;

    protected function getName( $prefix )
    {
        return $prefix . 'A';
    }
};

class B extends A
{
    public function do()
    {
        return $this->call( 'getName', 'B-' );
    }
};

This will check if there's a macro getName available and will call that instead of the getName() method:

// user code

(new B)->do(); // returns 'B-A'

A::macro( 'getName', function( $prefix ) {
   return $this->getName( $prefix ) . '-123';
} );

(new B)->do(); // returns 'B-A-123'

The original getName() method can still be used in the macro.

Sometimes, it may be necessary to remove macros from objects, especially when running automated tests. You can unset a macro by using:

class A
{
    use Aimeos\Macro\Macroable;
};

// add macro
A::macro( 'test', function() {
   return 'test';
} );

// remove macro
A::unmacro( 'test' );