# Sharing Code Across Multiple Targets In Compose Multiplatform

While working on my recent Compose Multiplatform app, [Sync Sphere](https://github.com/j-roskopf/SyncSphere), I added Desktop as a new target. Now supporting Android, iOS, and Desktop, there was some specific code that I wanted to share and have the same between Android and iOS, but differ on Desktop.

One solution is to have the code duplicated and live under `androidMain` and `iosMain` under the shared module. However, duplicating code like that isn't a good path forward for a multitude of reasons.

Adding a shared source set between Android and iOS was a perfect solution for me here, allowing me to have one definition for both mobile platforms.

Starting with the interface and class definitions in `commonMain`

```kotlin
interface RoomRepository {
    ...
}
```

```kotlin
expect class RoomRepositoryImpl(
    dictionary: Dictionary,
    // CrashReporting is also an interface that has expect / actual
    // implementations that are the same on mobile, but differ on Desktop
    crashReporting: CrashReporting,
) : RoomRepository
```

In `desktopMain`, I can define my `RoomRepositoryImpl` like normal

```kotlin
actual class RoomRepositoryImpl actual constructor(
    dictionary: Dictionary,
    crashReporting: CrashReporting,
) : RoomRepository {
    ... Desktop specific implementation
}
```

Now on the mobile side, I created a new folder under the `shared` module called `mobileMain`

![](https://cdn.hashnode.com/res/hashnode/image/upload/v1700231354562/5187e281-7d1f-4070-b8b3-6914466234d9.png align="center")

I register `mobileMain` as a source set in the `shared` module's build file like so:

```kotlin
        val mobileMain by creating {
            androidMain.dependsOn(this)
            iosMain.dependsOn(this)
            dependencies {
                dependsOn(commonMain)
                
                .. other dependencies
            }
        }
```

And now, I am able to put my common mobile implementation for `RoomRepository` that can be shared between Android and iOS!