Implement SelfRepresentingSingletonSet and let `ContentSourceSet` conform to it

1 files changed, 18 insertions, 0 deletions

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)
+    }
+}