Make IStructureElement contravariant.

src/main/java/com/gtnewhorizon/structurelib/structure/IStructureDefinition.java

@@ -67,7 +67,7 @@ public interface IStructureDefinition<T> {
      * @throws java.util.NoSuchElementException if the given structure piece is not found and the moon phase perfectly
      *                                          matches
      */
-    IStructureElement<T>[] getStructureFor(String name);
+    IStructureElement<? super T>[] getStructureFor(String name);
 
     boolean isContainedInStructure(String name, int offsetA, int offsetB, int offsetC);
 
@@ -356,7 +356,7 @@ public interface IStructureDefinition<T> {
      * @return true if iteration completed successfully.
      * @param <T> type of context object.
      */
-    static <T> boolean iterate(T object, ItemStack trigger, IStructureElement<T>[] elements, World world,
+    static <T> boolean iterate(T object, ItemStack trigger, IStructureElement<? super T>[] elements, World world,
             ExtendedFacing extendedFacing, int basePositionX, int basePositionY, int basePositionZ, int basePositionA,
             int basePositionB, int basePositionC, boolean hintsOnly, Boolean checkBlocksIfNotNullForceCheckAllIfTrue) {
         if (!world.isRemote && hintsOnly) {

src/main/java/com/gtnewhorizon/structurelib/structure/IStructureElement.java

@@ -28,6 +28,9 @@ import com.gtnewhorizon.structurelib.util.ItemStackPredicate.NBTMode;
 /**
  * Use StructureUtility to instantiate. These are the building blocks for your {@link IStructureDefinition}. It
  * represents what a particular element can be and how this particular element should be autoplaced.
+ *
+ * @param <T> Type of the context object. {@link IStructureElement} is contravariant over T, so parameters and fields of
+ *           type {@link IStructureElement} should be declared as {@code IStructureElement<? super T>}
  */
 public interface IStructureElement<T> {
 
@@ -213,7 +216,7 @@ public interface IStructureElement<T> {
      * Forget the messed up class dependency graph for now. this is just so convenient.
      */
     default IStructureElementNoPlacement<T> noPlacement() {
-        return new IStructureElementNoPlacement<T>() {
+        return new IStructureElementNoPlacement<>() {
 
             @Override
             public boolean check(T t, World world, int x, int y, int z) {

src/main/java/com/gtnewhorizon/structurelib/structure/IStructureWalker.java

@@ -21,23 +21,23 @@ public interface IStructureWalker<T> {
      * @param c       The relative C position of the element in structure-local coordinates (pre transform)
      * @return False to stop iterating, true to continue.
      */
-    boolean visit(IStructureElement<T> element, World world, int x, int y, int z, int a, int b, int c);
+    boolean visit(IStructureElement<? super T> element, World world, int x, int y, int z, int a, int b, int c);
 
-    default boolean blockNotLoaded(IStructureElement<T> element, World world, int x, int y, int z, int a, int b,
+    default boolean blockNotLoaded(IStructureElement<? super T> element, World world, int x, int y, int z, int a, int b,
             int c) {
         return false;
     }
 
     static <T> IStructureWalker<T> ignoreBlockUnloaded(IStructureWalker<T> walker) {
-        return new IStructureWalker<T>() {
+        return new IStructureWalker<>() {
 
             @Override
-            public boolean visit(IStructureElement<T> element, World world, int x, int y, int z, int a, int b, int c) {
+            public boolean visit(IStructureElement<? super T> element, World world, int x, int y, int z, int a, int b, int c) {
                 return walker.visit(element, world, x, y, z, a, b, c);
             }
 
             @Override
-            public boolean blockNotLoaded(IStructureElement<T> element, World world, int x, int y, int z, int a, int b,
+            public boolean blockNotLoaded(IStructureElement<? super T> element, World world, int x, int y, int z, int a, int b,
                     int c) {
                 return walker.visit(element, world, x, y, z, a, b, c);
             }
@@ -45,15 +45,15 @@ public interface IStructureWalker<T> {
     }
 
     static <T> IStructureWalker<T> skipBlockUnloaded(IStructureWalker<T> walker) {
-        return new IStructureWalker<T>() {
+        return new IStructureWalker<>() {
 
             @Override
-            public boolean visit(IStructureElement<T> element, World world, int x, int y, int z, int a, int b, int c) {
+            public boolean visit(IStructureElement<? super T> element, World world, int x, int y, int z, int a, int b, int c) {
                 return walker.visit(element, world, x, y, z, a, b, c);
             }
 
             @Override
-            public boolean blockNotLoaded(IStructureElement<T> element, World world, int x, int y, int z, int a, int b,
+            public boolean blockNotLoaded(IStructureElement<? super T> element, World world, int x, int y, int z, int a, int b,
                     int c) {
                 return true;
             }

src/main/java/com/gtnewhorizon/structurelib/structure/StructureDefinition.java

@@ -16,17 +16,17 @@ import com.gtnewhorizon.structurelib.util.Vec3Impl;
 
 public class StructureDefinition<T> implements IStructureDefinition<T> {
 
-    private final Map<Character, IStructureElement<T>> elements;
+    private final Map<Character, IStructureElement<? super T>> elements;
     private final Map<String, String> shapes;
-    private final Map<String, IStructureElement<T>[]> structures;
+    private final Map<String, IStructureElement<? super T>[]> structures;
     private final Map<String, Set<Vec3Impl>> occupiedSpaces;
 
     public static <B> Builder<B> builder() {
         return new Builder<>();
     }
 
-    private StructureDefinition(Map<Character, IStructureElement<T>> elements, Map<String, String> shapes,
-            Map<String, IStructureElement<T>[]> structures, Map<String, Set<Vec3Impl>> occupiedSpaces) {
+    private StructureDefinition(Map<Character, IStructureElement<? super T>> elements, Map<String, String> shapes,
+            Map<String, IStructureElement<? super T>[]> structures, Map<String, Set<Vec3Impl>> occupiedSpaces) {
         this.elements = elements;
         this.shapes = shapes;
         this.structures = structures;
@@ -40,7 +40,7 @@ public class StructureDefinition<T> implements IStructureDefinition<T> {
         private static final char C = '\uC000';
         private char d = '\uD000';
         private final Map<Vec3Impl, Character> navigates;
-        private final Map<Character, IStructureElement<T>> elements;
+        private final Map<Character, IStructureElement<? super T>> elements;
         private final Map<String, String> shapes;
         private final Map<String, Set<Vec3Impl>> occupiedSpaces;
 
@@ -51,7 +51,7 @@ public class StructureDefinition<T> implements IStructureDefinition<T> {
             occupiedSpaces = new HashMap<>();
         }
 
-        public Map<Character, IStructureElement<T>> getElements() {
+        public Map<Character, IStructureElement<? super T>> getElements() {
             return elements;
         }
 
@@ -181,18 +181,18 @@ public class StructureDefinition<T> implements IStructureDefinition<T> {
          * @deprecated use the unboxed version
          */
         @Deprecated
-        public Builder<T> addElement(Character name, IStructureElement<T> structurePiece) {
+        public Builder<T> addElement(Character name, IStructureElement<? super T> structurePiece) {
             elements.putIfAbsent(name, structurePiece);
             return this;
         }
 
-        public Builder<T> addElement(char name, IStructureElement<T> structurePiece) {
+        public Builder<T> addElement(char name, IStructureElement<? super T> structurePiece) {
             elements.putIfAbsent(name, structurePiece);
             return this;
         }
 
         public IStructureDefinition<T> build() {
-            Map<String, IStructureElement<T>[]> structures = compileStructureMap();
+            Map<String, IStructureElement<? super T>[]> structures = compileStructureMap();
             return new StructureDefinition<>(
                     new HashMap<>(elements),
                     new HashMap<>(shapes),
@@ -201,7 +201,7 @@ public class StructureDefinition<T> implements IStructureDefinition<T> {
         }
 
         @SuppressWarnings("unchecked")
-        private Map<String, IStructureElement<T>[]> compileElementSetMap() {
+        private Map<String, IStructureElement<? super T>[]> compileElementSetMap() {
             Set<Integer> missing = findMissing();
             if (missing.isEmpty()) {
                 return shapes.entrySet().stream().collect(
@@ -217,7 +217,7 @@ public class StructureDefinition<T> implements IStructureDefinition<T> {
         }
 
         @SuppressWarnings("unchecked")
-        private Map<String, IStructureElement<T>[]> compileStructureMap() {
+        private Map<String, IStructureElement<? super T>[]> compileStructureMap() {
             Set<Integer> missing = findMissing();
             if (missing.isEmpty()) {
                 return shapes.entrySet().stream().collect(
@@ -238,7 +238,7 @@ public class StructureDefinition<T> implements IStructureDefinition<T> {
         }
     }
 
-    public Map<Character, IStructureElement<T>> getElements() {
+    public Map<Character, IStructureElement<? super T>> getElements() {
         return elements;
     }
 
@@ -246,13 +246,13 @@ public class StructureDefinition<T> implements IStructureDefinition<T> {
         return shapes;
     }
 
-    public Map<String, IStructureElement<T>[]> getStructures() {
+    public Map<String, IStructureElement<? super T>[]> getStructures() {
         return structures;
     }
 
     @Override
-    public IStructureElement<T>[] getStructureFor(String name) {
-        IStructureElement<T>[] elements = structures.get(name);
+    public IStructureElement<? super T>[] getStructureFor(String name) {
+        IStructureElement<? super T>[] elements = structures.get(name);
         if (elements == null) throw new NoSuchElementException(name);
         return elements;
     }

src/main/java/com/gtnewhorizon/structurelib/structure/StructureUtility.java

@@ -3325,7 +3325,7 @@ public class StructureUtility {
         return (builder.toString().replaceAll("\"\"", "E"));
     }
 
-    static <T> boolean iterateV2(IStructureElement<T>[] elements, World world, ExtendedFacing extendedFacing,
+    static <T> boolean iterateV2(IStructureElement<? super T>[] elements, World world, ExtendedFacing extendedFacing,
             int basePositionX, int basePositionY, int basePositionZ, int basePositionA, int basePositionB,
             int basePositionC, IStructureWalker<T> predicate, String iterateType) {
         // change base position to base offset
@@ -3336,7 +3336,7 @@ public class StructureUtility {
         int[] abc = new int[] { basePositionA, basePositionB, basePositionC };
         int[] xyz = new int[3];
 
-        for (IStructureElement<T> element : elements) {
+        for (IStructureElement<? super T> element : elements) {
             if (element.isNavigating()) {
                 abc[0] = (element.resetA() ? basePositionA : abc[0]) + element.getStepA();
                 abc[1] = (element.resetB() ? basePositionB : abc[1]) + element.getStepB();

src/main/java/com/gtnewhorizon/structurelib/structure/SurvivalBuildStructureWalker.java

@@ -37,7 +37,7 @@ class SurvivalBuildStructureWalker<T> implements IStructureWalker<T> {
     }
 
     @Override
-    public boolean visit(IStructureElement<T> element, World world, int x, int y, int z, int a, int b, int c) {
+    public boolean visit(IStructureElement<? super T> element, World world, int x, int y, int z, int a, int b, int c) {
         env.offsetABC[0] = a;
         env.offsetABC[1] = b;
         env.offsetABC[2] = c;