By using Koin, you describe definitions in modules. In this section we will see how to declare, organize & link your modules.
What is a module?
A Koin module is a "space" to gather Koin definition. It's declared with the
Using several modules
Components doesn't have to be necessarily in the same module. A module is a logical space to help you organize your definitions, and can depend on definitions from other module. Definitions are lazy, and then are resolved only when a a component is requesting it.
Let's take an example, with linked components in separate modules:
Koin does't have any import concept. Koin definitions are lazy: a Koin definition is started with Koin container but is not instantiated. An instance is created only a request for its type has been done.
We just have to declare list of used modules when we start our Koin container:
Koin will then resolve dependencies from all given modules.
Linking modules strategies
As definitions between modules are lazy, we can use modules to implement different strategy implementation: declare an implementation per module.
Let's take an example, of a Repository and Datasource. A repository need a Datasource, and a Datasource can be implemented in 2 ways: Local or Remote.
We can declare those components in 3 modules: Repository and one per Datasource implementation:
Then we just need to launch Koin with the right combination of modules:
Overriding definition or module
Koin won't allow you to redefinition an already existing definition (type,name,path ...). You will an an error if you try this:
To allow definition overriding, you have to use the
Order matters when listing modules and overriding definitions. You must have your overriding definitions in last of your module list.