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- The IoC container creates an object of the specified class and also injects all the dependency objects through a constructor, a property or a method at run time and disposes it at the appropriate time. This is done so that we don't have to create and manage objects manually.
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Jun 5, 2021 · Yes you can use the container to get what's inside and send it to the function, but it can be a lot of boilerplate: f(ioc.service<ILogger>()); Same thing with your user type, you're using the container as a single thing containing the context, without using it's boilerplate reducing capabilities.
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The IoC container creates an object of the specified class and also injects all the dependency objects through a constructor, a property or a method at run time and disposes it at the appropriate time. This is done so that we don't have to create and manage objects manually.
- Dependency Injection with Interfaces
- Notes
- Mocking
- Dependecy Injection with Templates
- Hybrid Approach
- Summary
In the above example, Car is tightly coupled to V8Engine, meaning wecan't create a car without a concrete engine implementation. If we wantthe ability to swap various engines or use a mock engine during testing,we could reverse the dependency by creating an IEngine interface anddecoupling Car from the concrete V8Engine implementation. This way,we o...
A note on headers
Headers simply get textually included in each compilation unit by the#include directive. It is not mandatory to provide a header file foreach class declaration. If a class can be scoped to a single sourcefile, then it doesn't need a header declaration (for example theV8Engineclass above does not need a V8Engine.h header correspondingto the V8Engine.cpp). It is also a good idea to have public headers andinternal headers: public headers contain the public API surface and canbe included by other...
A note on interfaces
It's a good idea to declare a default virtual destructor: if a derivingtype has a destructor, it won't get called if we store an upcastpointer to the interface unless the interface declares a virtualdestructor. Note a destructor does not to be expicitly defined -compiler might generate a default one. MSVC compiler provides a __declspec(novtable)1 custom attributewhich tells the compiler not to generate a vtable for pure abstractclasses. This reduces code size. Below is the IEnginedeclaration...
A note on factory functions
When working with interfaces as opposed to concrete types, we usefactory functions to get object instances. Below is a possible namingconvention, taking object ownership into account: The first function, MakeFoo, returns a unique pointer, passingownership to the caller. Like in the example above, the unqiue_ptrcanbe moved into the object, which ends up owning it. Use a Make when eachcall creates a new instance. The second function implies there already exists an IFoo object whichis owned by s...
Since Car now works with an IEngineinterface, in test code we canmock the engine: Test.cpp: We can also expose Caras a simple interface, hiding itsimplementation details, in which case we would end up with thefollowing: ICar.h (publicly visible): Car.cpp: Test would become: Note this allows the caller to pass in any IEngine. We provide anout-of-the...
An alternative to the above is to use templates. In this case, we wouldhave to provide the implementation inside the header file, as code needsto be available when templates get instantiated: V8Engine.h (publicly visible): V8Engine.cpp: Car.h (publicly visible): Note Car is implemented in the header and V8Engine is also apublicly visible header. No...
We can use a hybrid approach if we don't need an externally injectedEngine. Say our component provides a V8Engine, a V6Engine, and wehave a MockEngineused during testing. We have the samecomponentization requirements but don't need to expose all the detailsto consumers. In that case we could have something like this: ICar.h (publicly visible): Car....
We decoupled Car from V8Engineand looked at three ways of injectingthe dependency: 1. Using interfaces, where dependency is injected at runtime duringobject creation 2. Using templates, where dependency is injected at compile-time duringtemplate instantiation 3. A hybrid approach which uses templates internally but exposes onlyinterfaces publicly E...
Jun 7, 2019 · There are 4 roles which cooperate to implement dependency-injection. The service object to be injected. The client object which depends on the service (s) being injected. The interface through which the client object uses the service (s). The injector which injects the service (s) into the client.
Sep 2, 2022 · Learn how to use C++'s static member variable initialization mechanism to implement a simple object auto-registration and dependency injection management framework.
IoC is a design principle which recommends the inversion of different kinds of controls in object-oriented design to achieve loose coupling between application classes.
The IoC principle helps in designing loosely coupled classes which make them testable, maintainable and extensible. Let's understand how IoC inverts the different kinds of control. Control Over the Flow of a Program. In a typical console application in C#, execution starts from the Main () function.
