# Defining and using a composite build

This sample shows how 2 Gradle builds that are normally developed separately and combined using binary integration can be wired together into a composite build with source integration. The `my-utils` multiproject build produces 2 different java libraries, and the `my-app` build produces an executable using functions from those libraries.

Note that the `my-app` build does not have direct dependencies on `my-utils`. Instead, it declares module dependencies on the libraries produced by `my-utils`:

```
dependencies {
    implementation "org.sample:number-utils:1.0"
    implementation "org.sample:string-utils:1.0"
}
```

### Using command-line composite build

When using a composite build, no shared repository is required for the builds, and no changes need to be made to the build scripts.

1. Change the sources of `Number.java`
2. Run the `my-app` application, including the `my-utils` build.

```
cd my-app
gradle --include-build ../my-utils run
```

Using *dependency substitution*, the module dependencies on the util libraries are replaced by project dependencies on `my-utils`.

### Converting `my-app` to a composite build

It's possible to make the above arrangement persistent, by making `my-app` a composite build that includes `my-utils`. 

```
cd my-app
echo "includeBuild '../my-utils'" >> settings.gradle
gradle run
```

With this configuration, the module dependencies from `my-app` to `my-utils` will always be substituted with project dependencies.

While simple, this approach has the downside of modifying the `my-app` build.

### Using separate composite build

It is also possible to create a separate composite build that includes both the `my-app` and `my-utils` builds.

```
rootProject.name='my-composite'

includeBuild '../my-app'
includeBuild '../my-utils'
```

Note that it is not yet possible to execute tasks in an included build from the command line. Instead, the build user must create delegating tasks in the composite.

```
task run {
    dependsOn gradle.includedBuild('my-app').task(':run')
}
```

```
cd composite
gradle run
```

We are working on a mechanism to permit tasks in included builds to be referred to directly on the command line. Stay tuned!
