example dependency injection

• Introduction
• Dev keynotes
• Fun facts
• How this project was built

Introduction

Purpose of this example is to show what dependency injection consists of and why its useful.

DI sometimes referred as IOC ( inversion of control ) states that isn't you responsible to create class instances but the service provider take care of that.

One think how can a program work if you can't create any object, of course in fact youll'do "inversely" through the use of a service builder in which you declare concrete object mapping to abstract, interfaces. Generally these service builder manage also the lifetime scope of the object as per singleton rather than scope ( they created on request and released when no more referenced ).

Use DI has some effects about the performance in object create, to benchmark the differences checkout the benchmark branch with git checkout benchmark. Follows comparision using about 800k calls of Service1 instantiation without DI ( direct service class instantiation ) and with ( using DI ) :

devel0@tuf:~/Documents/opensource/example-di$ dn run -c Release
DI BENCHMARK
  without : 00:00:00.2052394
  with    : 00:00:26.4634291

IoC allow to establish loose coupling between the layers you architect in your application. It allow you to ensure separation of concerns, enabling a sort of OOP encapsulation but at class/services rather than at methods or properties level.

DI is also used in the clean architecture pattern where there are benefits about the level of abstraction and modularity the application can achieve.

Dev keynotes

• add package references
• define service interface1 and interface2
• implement service1
• implement service2 using IoC to retrieve the service wanted ( the constructor will be called by the DI using approriate service instance )
• create a host builder assigning services mapping and run it

Execution

$ dotnet run
0.8722451498981519 + 0.7761152910999208 = 1.6483604409980728 ( matches )
info: Microsoft.Hosting.Lifetime[0]
      Application started. Press Ctrl+C to shut down.
info: Microsoft.Hosting.Lifetime[0]
      Hosting environment: Production
info: Microsoft.Hosting.Lifetime[0]
      Content root path: /home/devel0/Documents/opensource/example-di
0.8369665338633472 + 0.22125008465598472 = 1.058216618519332 ( matches )
0.9576765265593807 + 0.7209286927062147 = 1.6786052192655956 ( matches )
0.12588186914263888 + 0.1914292963073334 = 0.3173111654499723 ( matches )

Fun facts

Without changing the implementation of Service2 you can execute the application using another instance type of Service1 by substituting in the service mapping.

$ dotnet run
0.8001468290359208 + 0.212695476319962 = 1.0128423053558828 ( NOT matches )
info: Microsoft.Hosting.Lifetime[0]
      Application started. Press Ctrl+C to shut down.
info: Microsoft.Hosting.Lifetime[0]
      Hosting environment: Production
info: Microsoft.Hosting.Lifetime[0]
      Content root path: /home/devel0/Documents/opensource/example-di
0.8244152948560144 + 0.14512889210099444 = 0.9695441869570088 ( NOT matches )
0.6328938769401693 + 0.5873820115870374 = 1.2202758885272067 ( NOT matches )
0.9464424297386741 + 0.14904111339171255 = 1.0954835431303866 ( NOT matches )
0.19357539247737165 + 0.8354667215111734 = 1.029042113988545 ( NOT matches )

How this project was built

dn new console -n example-di
cd example-di
dotnet add package Microsoft.Extensions.DependencyInjection --version 7.0.0
dotnet add package Microsoft.Extensions.Hosting --version 7.0.0