Dependency Injection

CLASS … DEFINITION … .
	DATA(lo_cash_provider) = NEW cl_cash_provider( ).
ENDCLASS.

👆🏽 This here is a Dependency.

Design pattern in which, instead of creating the object ourselves in our code, we let some other entity create the object and "inject" into our class.

⇒ Dependency injection implements OO Design Principles#Inversion of Control.

The dependency can be injected via:

constructor
setter method
parameter
backdoor

Constructor Injection

CLASS … DEFINITION … .
	
PUBLIC SECTION.
	METHODS constructor
		IMPORTING i_cash_provider TYPE REF TO if_cash_provider OPTIONAL.

PRIVATE SECTION.
	DATA m_cash_provider TYPE REF TO if_cash_provider.
…
ENDCLASS.


CLASS … IMPLEMENTATION.
METHOD constructor.
	m_cash_provider = COND #( WHEN i_cash_provider IS BOUND
			   				  THEN i_cash_provider
							  ELSE NEW cl_cash_provider( ) ).
ENDMETHOD.
…
ENDCLASS.

Setter Injection

CLASS … DEFINITION … .
PUBLIC SECTION.
	METHODS set_cash_provider 
		IMPORTING i_cash_provider TYPE REF TO if_cash_provider.
PRIVATE SECTION.
	DATA m_cash_provider TYPE REF TO if_cash_provider.
…
ENDCLASS.

CLASS … IMPLEMENTATION.
METHOD set_cash_provider.
	m_cash_provider = i_cash_provider.
ENDMETHOD.
…
ENDCLASS.

Parameter Injection

CLASS … DEFINITION … .
PUBLIC SECTION.
	METHODS get_amount_in_coins
		IMPORTING
			i_amount TYPE i
			i_cash_provider TYPE REF TO if_cash_provider OPTIONAL
		RETURNING VALUE(r_value) TYPE i.
PRIVATE SECTION.
	DATA m_cash_provider TYPE REF TO if_cash_provider.
…
ENDCLASS.

CLASS … IMPLEMENTATION.
METHOD get_amount_in_coins.
	DATA(cash_provider) = CAST if_cash_provider(
							COND #( WHEN i_cash_provider IS BOUND
									THEN i_cash_provider
									ELSE NEW cl_cash_provider( ) ) ).
…
ENDMETHOD.
…
ENDCLASS

Backdoor Injection

Injection done using OOP#Friend Class.

CLASS … DEFINITION … .
PRIVATE SECTION.
	DATA m_cash_provider TYPE REF TO if_cash_provider.
…
ENDCLASS.

CLASS ltc_get_amount_in_coins DEFINITION DEFERRED.
CLASS cl_money_machine DEFINITION
LOCAL FRIENDS ltc_get_amount_in_coins.

CLASS ltc_get_amount_in_coins DEFINITION FOR TESTING … .
…
ENDCLASS.

CLASS ltc_get_amount_in_coins IMPLEMENTATION.
METHOD setup.
	"given
	m_cut = NEW #( ).
	m_cut->m_cash_provider = NEW ltd_cash_provider( ).
ENDMETHOD.
ENDCLASS.

Field Injection

When a field in a class is directly injected into upon initialization (by a framework or library).

Not generally recommended though.