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# Groovy Closures in the Gradle Kotlin DSL
Most third party plugins are written in groovy with the expectation that closures will
be passed as arguments. In order to provide a way to construct closures while preserving kotlin's
strong typing two helper methods exist:
- `closureOf<...> {...}`
- `delegateClosureOf<...> {...}`.
Both methods are useful in different circumstances and depend upon the method you are passing the
closure into. To understand the difference between the two types of closures [this document](http://groovy-lang.org/closures.html)
may be helpful.
Some plugins expect only closures:
```kotlin
val tests = mapOf(
"API" to "src/test/resources/api/ApiTestSuite.xml",
"System" to "src/test/resources/system/SystemTestSuite.xml"
)
val testTasks = tests.map {
val (name, path) = it
task<Test>("test$name") {
val testNGOptions = closureOf<TestNGOptions> {
suites(path)
}
useTestNG(testNGOptions)
}
}
```
In other cases, like in the [Gretty Plugin](https://github.com/akhikhl/gretty) when configuring farms,
the plugin expects a delegate closure:
```kotlin
configure<FarmsExtension> {
farm("OldCoreWar", delegateClosureOf<FarmExtension> {
// Config for the war here
}
}
```
There sometimes isn't a good way to tell, from looking at the source code, which version to use.
Usually, if you get a `NullPointerException` with the `closureOf`, using `delegateClosureOf`
will resolve the problem.
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