fileCollections[i] = (FileCollectionInternal) artifactSets[i].getFiles();
        }
        files = new UnionFileCollection(taskDependencyFactory, fileCollections);
    }

    @Override
    public FileCollection getFiles() {
        return files;
    }

        private final ImmutableList<FileCollectionInternal> fileCollections;

        public ResolvedItemsCollector(ImmutableList<FileCollectionInternal> fileCollections) {
            this.fileCollections = fileCollections;
        }

        @Override
        public boolean isEmpty() {
            return fileCollections.isEmpty();
        }

        @Override

public class DependencyFilesNotationConverter implements NotationConverter<FileCollection, FileCollectionDependency> {
    private final Instantiator instantiator;

    public DependencyFilesNotationConverter(Instantiator instantiator) {
        this.instantiator = instantiator;
    }

    @Override
    public void describe(DiagnosticsVisitor visitor) {
        visitor.candidate("FileCollections").example("files('some.jar', 'someOther.jar')");
    }

dependencies {
    api(projects.baseServices)
    api(projects.configurationCacheBase)
    api(projects.core)
    api(projects.coreApi)
    api(projects.dependencyManagement)
    api(projects.fileCollections)
    api(projects.flowServices)
    api(projects.graphSerialization)
    api(projects.stdlibJavaExtensions)
    api(projects.logging)
    api(projects.modelCore)
    api(projects.snapshots)

    implementation(libs.ant) {
        because("only used for DateUtils")
    }
    implementation(libs.commonsLang)
    implementation(libs.kryo)
    implementation(libs.slf4jApi)

    testImplementation(projects.fileCollections)
    testImplementation(projects.enterpriseOperations)
    testImplementation(testFixtures(projects.baseServices))
    testImplementation(testFixtures(projects.core))
    testImplementation(testFixtures(projects.logging))

    implementation(projects.dependencyManagementSerializationCodecs)
    implementation(projects.enterpriseOperations)
    implementation(projects.execution)
    implementation(projects.fileCollections)
    implementation(projects.fileWatching)
    implementation(projects.files)
    implementation(projects.flowServices)
    implementation(projects.functional)
    implementation(projects.graphSerialization)

====
include::sample[dir="snippets/files/fileCollections/kotlin",files="build.gradle.kts[tags=closure]"]
include::sample[dir="snippets/files/fileCollections/groovy",files="build.gradle[tags=closure]"]
====

----
$ gradle -q list
include::{snippetsPath}/files/fileCollections/tests/fileCollectionsWithClosure.out[]
----

     *
     * @param collection The other collection. Should not be null.
     * @return A new collection containing the union.
     */
    FileCollection plus(FileCollection collection);

    /**
     * <p>Returns a {@code FileCollection} which contains the difference between this collection and the given
     * collection. The returned collection is live, and tracks changes to both source collections.</p>
     *

        def calculated = Stub(MinimalFileSet)
        def fileCollection = new CalculatedTaskInputFileCollection(taskDependencyFactory, ":task", calculated)

        calculated.displayName >> "<files>"

        given:
        fileCollection.prepareValue()
        fileCollection.files
        fileCollection.cleanupValue()

        when:
        fileCollection.files

        then:

        "FileCollection += FileCollection" | "+="      | "FileCollection" | 'files("a.txt")'  | '[a.txt]'
        "FileCollection << FileCollection" | "<<"      | "FileCollection" | 'files("a.txt")'  | unsupportedWithCause("No signature of method")