Typos and further change re comments

This commit is contained in:
happyaccidents
2013-11-29 09:46:15 +00:00
committed by Josh Lockhart
parent aaebe65095
commit 4bdbd868c3
2 changed files with 18 additions and 18 deletions

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## Complex Problem {#complex_problem_title}
If you have ever read about Dependency Injection then you have probably seen the terms *"Inversion of Control"* or *"Dependency Inversion Principle"*.
If you have ever read about Dependency Injection then you have probably seen the terms *"Inversion of Control"* or *"Dependency Inversion Principle"*.
These are the complex problems that Dependency Injection solves.
### Inversion of Control
Inversion of Control is as it says, "inverting the control" of a system by keeping organisational control entirely separate from our objects.
Inversion of Control is as it says, "inverting the control" of a system by keeping organisational control entirely separate from our objects.
In terms of Dependency Injection, this means loosening our dependencies by controlling and instantiating them elsewhere in the system.
For years, PHP frameworks have been achieving Inversion of Control, however, the question became, which part of control
are you inverting, and where to? For example, MVC frameworks would generally provide a super object or base controller that other
controllers must extend to gain access to it's dependencies. This **is** Inversion of Control, however, instead of loosening
For years, PHP frameworks have been achieving Inversion of Control, however, the question became, which part of control
are you inverting, and where to? For example, MVC frameworks would generally provide a super object or base controller that other
controllers must extend to gain access to its dependencies. This **is** Inversion of Control, however, instead of loosening
dependencies, this method simply moved them.
Dependency Injection allows us to more elegantly solve this problem by only injecting the dependencies we need, when we need them,
Dependency Injection allows us to more elegantly solve this problem by only injecting the dependencies we need, when we need them,
without the need for any hard coded dependencies at all.
### Dependency Inversion Principle
Dependency Inversion Principle is the "D" in the S.O.L.I.D set of object oriented design principles that states one should
*"Depend on Abstractions. Do not depend on concretions."*. Put simply, this means our dependencies should be interfaces/contracts or abstract
Dependency Inversion Principle is the "D" in the S.O.L.I.D set of object oriented design principles that states one should
*"Depend on Abstractions. Do not depend on concretions."*. Put simply, this means our dependencies should be interfaces/contracts or abstract
classes rather than concrete implementations. We can easily refactor the above example to follow this principle.
{% highlight php %}
@@ -45,12 +45,12 @@ interface AdapterInterface {}
class MysqlAdapter implements AdapterInterface {}
{% endhighlight %}
There are several benefits to the Database class now depending on an interface rather than a concretion.
There are several benefits to the `Database` class now depending on an interface rather than a concretion.
Consider that you are working in a team and the adapter is being worked on by a colleague. In our first example, we would have
to wait for said colleague to finish the adapter before we could properly mock it for our unit tests. Now that the dependency
Consider that you are working in a team and the adapter is being worked on by a colleague. In our first example, we would have
to wait for said colleague to finish the adapter before we could properly mock it for our unit tests. Now that the dependency
is an interface/contract we can happily mock that interface knowing that our colleague will build the adapter based on that contract.
An even bigger benefit to this method is that our code is now much more scalable. If a year down the line we decide that we
want to migrate to a different type of database, we can write an adapter that implements the original interface and inject that instead,
An even bigger benefit to this method is that our code is now much more scalable. If a year down the line we decide that we
want to migrate to a different type of database, we can write an adapter that implements the original interface and inject that instead,
no more refactoring would be required as we can ensure that the adapter follows the contract set by the interface.

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## Containers {#containers_title}
The first thing you should understand about Dependency Injection Containers is that they are not the same thing as Dependency
Injection. A container is a convenience utility that helps us implement Dependency Injection, however, they can be and often
are misused to implement an anti pattern, Service Location. Using a container as a Service Locator within your classes arguably
creates a harder dependency on the container than the dependency you are replacing. It also makes your code much less transparent
The first thing you should understand about Dependency Injection Containers is that they are not the same thing as Dependency
Injection. A container is a convenience utility that helps us implement Dependency Injection, however, they can be and often
are misused to implement an anti-pattern, Service Location. Injecting a DI container as a Service Locator in to your classes arguably
creates a harder dependency on the container than the dependency you are replacing. It also makes your code much less transparent
and ultimately harder to test.
Most modern frameworks have their own Dependency Injection Container that allows you to wire your dependencies together through configuration.
Most modern frameworks have their own Dependency Injection Container that allows you to wire your dependencies together through configuration.
What this means in practice is that you can write application code that is as clean and de-coupled as the framework it is built on.