Scopes

We learned what settings and tasks are. Scopes ( aka Configurations ) are namespaces for settings and tasks. We use these namespaces to reuse existing tasks.

SBT provides a bunch of Scopes by default.

• Compile- compilation scope
• Test- test scope
• IntegrationTest- integration test scope. Not configured by default
• ThisBuild- configures this setting or task everywhere in your build

Every scope has a string representation, which can be used in the SBT shell to access a setting or task in a specific scope.

Using scopes in the shell

The compiletask is defined in the Compileand Testscope. The compiletask in the Compilescope only compiles your sources files in src/main/scala. The compiletask in the Testscope depends on the compiletask in the Compilescope and compiles your sources in src/test/scala.

Start the SBT shell

$ sbt

Compile the test sources

> test:compile

From the command you can see the general structure

<scope>:<task>

The scope is on the left side of the colon and the task or setting on the right.

Scope task and settings

We can access the output of a setting or task with the .value operator. To access the the output in a specific scope we can use the in operator. The same operator is used when defining settings or task in a specific scope. As an example, we will change to target setting in the Test scope. The target setting returns a java.io.File directory where tasks can put generated content into.

target in Test := target.value / "test-output"

We can see our changes when we start the SBT shell

$ sbt

And inspect the different target values.

> show target
[info] /home/sbt/myproject/target
> show test:target
[info] /home/sbt/myproject/target/test-output

Accessing works the same way

(target in Test).value

Scope axes

Configurations are not the only way to scope a setting or task. Projects and settings/tasks themselves can be used to scope settings and tasks. The API show before is only a special case of the general scoping API:

taskOrSetting in (aProject, aScope, aTaskOrSetting)

Exercise

The run task runs your application if there is a single main class or you explicitly configure the mainClass setting.

Beginner

Set the mainClass for Test scope to the mainClass detected in the Compile scope. You should be able to run

> test:run

Advanced

The run task runs your application if there is a single main class or you explicitly configure the mainClass setting. By default it uses the sbt jvm process to run your application. With the fork setting this behaviour can be changed.

Change the fork setting to true in the Compile scope and only for the run task. In the sbt shell

run

should create a new jvm process.