IoC concepts: Dependency

As part of prepar­ing for release of Wind­sor 3.1 I decided to revisit parts of Windsor’s doc­u­men­ta­tion and try to make it more approach­able to some com­pletely new to IoC. This and few previous posts are excerpts from that new doc­u­men­ta­tion. As such I would appre­ci­ate any feed­back, espe­cially around how clearly the con­cepts in ques­tion are explained for some­one who had no prior expo­sure to them.


We’re almost there. To get the full picture we need to talk about dependencies first.

A component working to fulfil its service is not living in a vacuum. Just lie a coffee shop depends on services provided by utility companies (electricity), its suppliers (to get the beans, milk etc) most components will end up delegating non-essential aspects of what they’re doing to others.

Now let me repeat one thing just to make sure it’s obvious. Components depend on services of other components. This allows for nicely decoupled code where your coffee shop is not burdened with details of how the milk delivery guy operates.

In addition to depending on other component’s services your components will also sometimes use things that are not components themselves. Things like connectionStrings, names of servers, values of timeouts and other configuration parameters are not services (as we discussed previously) yet are valid (and common) dependencies of a component.

In C# terms your component will declare what dependencies it requires usually via constructor arguments or settable properties. In some more advanced scenarios dependencies of a component may have nothing to do with the class you used as implementation (remember, the concept of a component is not the same as a class that might be used as its implementation), for example when you’re applying interceptors. This is advanced stuff however so you don’t have to concern yourself with it if you’re just starting out.

Putting it all together

So now lets put it all together. To effectively use a container we’re dealing with small components, exposing small, well defined, abstract services, depending on services provided by other components, and on some configuration values to fulfil contracts of their services.

You will end up having many small, decoupled components, which will allow you to rapidly change and evolve your application limiting the scope of changes, but the downside of that is you’ll end up having plenty small classes with multiple dependencies that someone will have to manage.

That is the job of a container.