1 files changed, 29 insertions, 0 deletions
diff --git a/src/main/java/gregtech/api/objects/CollectorUtils.java b/src/main/java/gregtech/api/objects/CollectorUtils.java
new file mode 100644
index 0000000000..3f89ad0773
--- /dev/null
+++ b/src/main/java/gregtech/api/objects/CollectorUtils.java
@@ -0,0 +1,29 @@
+package gregtech.api.objects;
+
+import java.util.Map;
+import java.util.function.BiFunction;
+import java.util.function.BinaryOperator;
+import java.util.function.Function;
+import java.util.function.Supplier;
+import java.util.stream.Collector;
+import java.util.stream.Collectors;
+
+public class CollectorUtils {
+    /**
+     * Returns a merge function, suitable for use in
+     * {@link Map#merge(Object, Object, BiFunction) Map.merge()} or
+     * {@link Collectors#toMap(Function, Function, BinaryOperator) toMap()}, which always
+     * throws {@code IllegalStateException}.  This can be used to enforce the
+     * assumption that the elements being collected are distinct.
+     *
+     * @param <T> the type of input arguments to the merge function
+     * @return a merge function which always throw {@code IllegalStateException}
+     */
+    public static <T> BinaryOperator<T> throwingMerger() {
+        return (u,v) -> { throw new IllegalStateException(String.format("Duplicate key %s", u)); };
+    }
+
+    public static <K, V, E extends Map.Entry<K, V>, M extends Map<K, V>> Collector<E, ?, M> entriesToMap(Supplier<M> mapSupplier) {
+        return Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, CollectorUtils.throwingMerger(), mapSupplier);
+    }
+}