Definition “Inversion of control” What does inversion of control mean?
Inversion of Control is a design principle or development paradigm in which the control flow of an application is outsourced to another location. A common example is that a framework takes over the control of certain parts of the program.
The programming principle Inversion of Control (IoC) reverses the conventional control flow of a program. Without IoC, the control flow would be such that the program code written by the developer calls up resources from libraries to use them. The objects are statically connected to each other.
If the control flow is reversed by inversion of Control, the code from the framework dynamically accesses the developer’s custom code instead. Framework and custom code are now only loosely coupled.
Benefits of Inversion of Control
Many advantages of the control reversal are related to the fact that, as already mentioned, dependencies are only loosely coupled to each other. Or more generally, the implementation and the execution of a task are decoupled from each other by inversion of Control.
This means that the reusable parts of the code that are useful more often and in different places of the program can be developed independently of the places where a specific problem is solved. Although they may only lead to the desired result together, they do not have to be developed or adapted at the same time. Further thought, this has the advantage that it becomes easier to switch between different implementations (e.g. from a framework).
Programs are also easier to design modularly, especially when it comes to complex code. In other words, it is easier to make modules more independent of the rest of the code. For example, more focus can be placed on modules that are compact and tailored to a specific task. There are also fewer unforeseen effects on the entire project when a single module is replaced. Likewise, testing the software can become easier if the components are kept better isolated from each other.
Disadvantages of Inversion of Control
Reversing the control flow is in many cases a sensible option to keep a complex system maintainable and clear. Nevertheless, one should carefully check whether it is really the right approach. Because IoC also means a higher effort in the design, implementation and maintenance of software.
There are scenarios in which this additional work does not pay off or is currently in conflict with the higher quality criteria of the project. If, for example, the top priority is to quickly see the first results or to be able to prove the suitability of a concept, it may be better to switch to Inversion of Control at a later date.
Examples of design patterns based on Inversion of Control:
Dependency injection: An object does not manage its dependencies itself, but gets them assigned by a separate piece of code. The dependencies are stored on a separate component and can thus be managed more clearly.
Service Locator Pattern: The Service Locator, a central register, serves as an intermediary and, upon request, passes on all the information that is needed for the requested task. In this way, different parts of a library can exist encapsulated from each other and can still be connected via the service locator.
Strategy Patterns: At runtime, one of several algorithms is selected via an intermediary class depending on the context.
As of 30.10.2020
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