Implement SelfRepresentingSingletonSet and let `ContentSourceSet` conform to it

2 files changed, 20 insertions, 10 deletions

diff --git a/core/src/main/kotlin/model/ContentSourceSet.kt b/core/src/main/kotlin/model/ContentSourceSet.kt
index 6eee4c94..8a1bf53c 100644
--- a/core/src/main/kotlin/model/ContentSourceSet.kt
+++ b/core/src/main/kotlin/model/ContentSourceSet.kt
@@ -3,28 +3,20 @@ package org.jetbrains.dokka.model
 import org.jetbrains.dokka.DokkaConfiguration.DokkaSourceSet
 import org.jetbrains.dokka.DokkaSourceSetID
 import org.jetbrains.dokka.Platform
+import org.jetbrains.dokka.utilities.SelfRepresentingSingletonSet
 
 data class ContentSourceSet(
     val sourceSetIDs: CompositeSourceSetID,
     val displayName: String,
     val analysisPlatform: Platform
-) {
+) : SelfRepresentingSingletonSet<ContentSourceSet> {
     constructor(sourceSet: DokkaSourceSet) : this(
         sourceSetIDs = CompositeSourceSetID(sourceSet.sourceSetID),
         displayName = sourceSet.displayName,
         analysisPlatform = sourceSet.analysisPlatform
     )
-
-    operator fun contains(sourceSetID: DokkaSourceSetID): Boolean {
-        return sourceSetID in sourceSetIDs
-    }
-
-    operator fun contains(sourceSet: DokkaSourceSet): Boolean {
-        return sourceSet.sourceSetID in this
-    }
 }
 
-
 fun DokkaSourceSet.toContentSourceSet(): ContentSourceSet = ContentSourceSet(this)
 
 fun Iterable<DokkaSourceSet>.toContentSourceSets(): Set<ContentSourceSet> = map { it.toContentSourceSet() }.toSet()
diff --git a/core/src/main/kotlin/utilities/SelfRepresentingSingletonSet.kt b/core/src/main/kotlin/utilities/SelfRepresentingSingletonSet.kt
new file mode 100644
index 00000000..d384bda4
--- /dev/null
+++ b/core/src/main/kotlin/utilities/SelfRepresentingSingletonSet.kt
@@ -0,0 +1,18 @@
+package org.jetbrains.dokka.utilities
+
+interface SelfRepresentingSingletonSet<T : SelfRepresentingSingletonSet<T>> : Set<T> {
+    override val size: Int get() = 1
+
+    override fun contains(element: T): Boolean = this == element
+
+    override fun containsAll(elements: Collection<T>): Boolean =
+        if (elements.isEmpty()) true
+        else elements.all { this == it }
+
+    override fun isEmpty(): Boolean = false
+
+    override fun iterator(): Iterator<T> = iterator {
+        @Suppress("UNCHECKED_CAST")
+        yield(this@SelfRepresentingSingletonSet as T)
+    }
+}