Fix some syntaxes overwriting variable list indices and add new helper method for changing expressions.

src/main/java/ch/njol/skript/effects/EffEnchant.java

@@ -18,11 +18,6 @@
  */
 package ch.njol.skript.effects;
 
-import org.bukkit.enchantments.Enchantment;
-import org.bukkit.event.Event;
-import org.bukkit.inventory.ItemStack;
-import org.jetbrains.annotations.Nullable;
-
 import ch.njol.skript.Skript;
 import ch.njol.skript.aliases.ItemType;
 import ch.njol.skript.classes.Changer.ChangeMode;
@@ -36,6 +31,11 @@
 import ch.njol.skript.lang.SkriptParser.ParseResult;
 import ch.njol.skript.util.EnchantmentType;
 import ch.njol.util.Kleenean;
+import org.bukkit.event.Event;
+import org.bukkit.inventory.ItemStack;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.function.Function;
 
 /**
  * @author Peter Güttinger
@@ -72,29 +72,26 @@ public boolean init(Expression<?>[] exprs, int matchedPattern, Kleenean isDelaye
 
 	@Override
 	protected void execute(Event event) {
-		ItemType[] items = this.items.getArray(event);
-		if (items.length == 0) // short circuit
-			return;
+		Function<ItemType, ItemType> changeFunction;
 
 		if (enchantments != null) {
 			EnchantmentType[] types = enchantments.getArray(event);
 			if (types.length == 0)
 				return;
-			for (ItemType item : items) {
-				for (EnchantmentType type : types) {
-					Enchantment enchantment = type.getType();
-					assert enchantment != null;
-					item.addEnchantments(new EnchantmentType(enchantment, type.getLevel()));
-				}
-			}
+			changeFunction = item -> {
+				item.addEnchantments(types);
+				return item;
+			};
 		} else {
-			for (ItemType item : items) {
+			changeFunction = item -> {
 				item.clearEnchantments();
-			}
+				return item;
+			};
 		}
-		this.items.change(event, items.clone(), ChangeMode.SET);
+
+		this.items.changeInPlace(event, changeFunction);
 	}
-	
+
 	@Override
 	public String toString(@Nullable Event event, boolean debug) {
 		return enchantments == null ? "disenchant " + items.toString(event, debug) : "enchant " + items.toString(event, debug) + " with " + enchantments;

src/main/java/ch/njol/skript/effects/EffReplace.java

@@ -36,9 +36,11 @@
 import org.bukkit.event.Event;
 import org.bukkit.inventory.Inventory;
 import org.bukkit.inventory.ItemStack;
+import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
 import java.util.Map;
+import java.util.function.Function;
 import java.util.regex.Matcher;
 
 @Name("Replace")
@@ -106,20 +108,9 @@ private void replace(Event event, Object[] needles, Expression<?> haystackExpr)
 		if (replacement == null || haystack == null || haystack.length == 0 || needles == null || needles.length == 0)
 			return;
 		if (replaceString) {
-			if (replaceFirst) {
-				for (int x = 0; x < haystack.length; x++)
-					for (Object n : needles) {
-						assert n != null;
-						haystack[x] = StringUtils.replaceFirst((String)haystack[x], (String)n, Matcher.quoteReplacement((String)replacement), caseSensitive);
-					}
-			} else {
-				for (int x = 0; x < haystack.length; x++)
-					for (Object n : needles) {
-						assert n != null;
-						haystack[x] = StringUtils.replace((String) haystack[x], (String) n, (String) replacement, caseSensitive);
-					}
-			}
-			haystackExpr.change(event, haystack, ChangeMode.SET);
+			Function<String, String> replaceFunction = getReplaceFunction(needles, (String) replacement);
+			//noinspection unchecked
+			((Expression<String>) haystackExpr).changeInPlace(event, replaceFunction);
 		} else {
 			for (Inventory inv : (Inventory[]) haystack)
 				for (ItemType needle : (ItemType[]) needles)
@@ -137,14 +128,36 @@ private void replace(Event event, Object[] needles, Expression<?> haystackExpr)
 					}
 		}
 	}
-
+
+	private @NotNull Function<String, String> getReplaceFunction(Object[] needles, String replacement) {
+		Function<String, String> replaceFunction;
+		if (replaceFirst) {
+			replaceFunction = haystackString -> {
+				for (Object needle : needles) {
+					assert needle != null;
+					haystackString = StringUtils.replaceFirst(haystackString, (String) needle, Matcher.quoteReplacement(replacement), caseSensitive);
+				}
+				return haystackString;
+			};
+		} else {
+			replaceFunction = haystackString -> {
+				for (Object needle : needles) {
+					assert needle != null;
+					haystackString = StringUtils.replace(haystackString, (String) needle, replacement, caseSensitive);
+				}
+				return haystackString;
+			};
+		}
+		return replaceFunction;
+	}
+
 	@Override
 	public String toString(@Nullable Event event, boolean debug) {
 		if (replaceFirst)
-			return "replace first " + needles.toString(event, debug) + " in " + haystack.toString(event, debug) + " with " + replacement.toString(event, debug)
-					+ "(case sensitive: " + caseSensitive + ")";
-		return "replace " + needles.toString(event, debug) + " in " + haystack.toString(event, debug) + " with " + replacement.toString(event, debug)
-				+ "(case sensitive: " + caseSensitive + ")";
+			return "replace first " + needles.toString(event, debug) + " in " + haystack.toString(event, debug) +
+					" with " + replacement.toString(event, debug) + "(case sensitive: " + caseSensitive + ")";
+		return "replace " + needles.toString(event, debug) + " in " + haystack.toString(event, debug) +
+				" with " + replacement.toString(event, debug) + "(case sensitive: " + caseSensitive + ")";
 	}
 
 }

src/main/java/ch/njol/skript/expressions/ExprVectorLength.java

@@ -18,18 +18,20 @@
  */
 package ch.njol.skript.expressions;
 
-import ch.njol.util.VectorMath;
-import org.bukkit.event.Event;
-import org.bukkit.util.Vector;
-import org.jetbrains.annotations.Nullable;
-
 import ch.njol.skript.classes.Changer.ChangeMode;
 import ch.njol.skript.doc.Description;
 import ch.njol.skript.doc.Examples;
 import ch.njol.skript.doc.Name;
 import ch.njol.skript.doc.Since;
 import ch.njol.skript.expressions.base.SimplePropertyExpression;
+import ch.njol.skript.lang.Expression;
+import ch.njol.util.VectorMath;
 import ch.njol.util.coll.CollectionUtils;
+import org.bukkit.event.Event;
+import org.bukkit.util.Vector;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.function.Function;
 
 @Name("Vectors - Length")
 @Description("Gets or sets the length of a vector.")
@@ -61,39 +63,49 @@ public Class<?>[] acceptChange(ChangeMode mode) {
 	}
 
 	@Override
-	public void change(Event event, @Nullable Object[] delta, ChangeMode mode) {
+	public void change(Event event, Object @Nullable [] delta, ChangeMode mode) {
 		assert delta != null;
-		final Vector[] vectors = getExpr().getArray(event);
 		double deltaLength = ((Number) delta[0]).doubleValue();
+
+		Function<Vector, Vector> changeFunction;
 		switch (mode) {
 			case REMOVE:
 				deltaLength = -deltaLength;
 				//$FALL-THROUGH$
 			case ADD:
-				for (Vector vector : vectors) {
-					if (VectorMath.isZero(vector) || (deltaLength < 0 && vector.lengthSquared() < deltaLength * deltaLength)) {
+				double finalDeltaLength = deltaLength;
+				double finalDeltaLengthSquared = deltaLength * deltaLength;
+				changeFunction = vector -> {
+					if (VectorMath.isZero(vector) || (finalDeltaLength < 0 && vector.lengthSquared() < finalDeltaLengthSquared)) {
 						vector.zero();
 					} else {
-						double newLength = deltaLength + vector.length();
+						double newLength = finalDeltaLength + vector.length();
 						if (!vector.isNormalized())
 							vector.normalize();
 						vector.multiply(newLength);
 					}
-				}
+					return vector;
+				};
 				break;
 			case SET:
-				for (Vector vector : vectors) {
-					if (deltaLength < 0 || VectorMath.isZero(vector)) {
+				double finalDeltaLength1 = deltaLength;
+				changeFunction = vector -> {
+					if (finalDeltaLength1 < 0 || VectorMath.isZero(vector)) {
 						vector.zero();
 					} else {
 						if (!vector.isNormalized())
 							vector.normalize();
-						vector.multiply(deltaLength);
+						vector.multiply(finalDeltaLength1);
 					}
-				}
+					return vector;
+				};
 				break;
+			default:
+				return;
 		}
-		getExpr().change(event, vectors, ChangeMode.SET);
+
+		//noinspection unchecked,DataFlowIssue
+		((Expression<Vector>) getExpr()).changeInPlace(event, changeFunction);
 	}
 
 	@Override

src/main/java/ch/njol/skript/expressions/ExprVectorXYZ.java

@@ -18,10 +18,6 @@
  */
 package ch.njol.skript.expressions;
 
-import org.bukkit.event.Event;
-import org.bukkit.util.Vector;
-import org.jetbrains.annotations.Nullable;
-
 import ch.njol.skript.classes.Changer;
 import ch.njol.skript.classes.Changer.ChangeMode;
 import ch.njol.skript.doc.Description;
@@ -33,6 +29,11 @@
 import ch.njol.skript.lang.SkriptParser.ParseResult;
 import ch.njol.util.Kleenean;
 import ch.njol.util.coll.CollectionUtils;
+import org.bukkit.event.Event;
+import org.bukkit.util.Vector;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.function.Function;
 
 @Name("Vectors - XYZ Component")
 @Description("Gets or changes the x, y or z component of a vector.")
@@ -84,39 +85,45 @@ public Class<?>[] acceptChange(ChangeMode mode) {
 	@Override
 	public void change(Event event, @Nullable Object[] delta, ChangeMode mode) {
 		assert delta != null;
-		Vector[] vectors = getExpr().getArray(event);
-		if (vectors.length == 0)
-			return;
 		double deltaValue = ((Number) delta[0]).doubleValue();
+		Function<Vector, Vector> changeFunction;
 		switch (mode) {
 			case REMOVE:
 				deltaValue = -deltaValue;
 				//$FALL-THROUGH$
 			case ADD:
-				for (Vector vector : vectors) {
-					if (axis == 0)
-						vector.setX(vector.getX() + deltaValue);
-					else if (axis == 1)
-						vector.setY(vector.getY() + deltaValue);
-					else
-						vector.setZ(vector.getZ() + deltaValue);
-				}
+				double finalDeltaValue1 = deltaValue;
+				changeFunction = vector -> {
+					if (axis == 0) {
+						vector.setX(vector.getX() + finalDeltaValue1);
+					} else if (axis == 1) {
+						vector.setY(vector.getY() + finalDeltaValue1);
+					} else {
+						vector.setZ(vector.getZ() + finalDeltaValue1);
+					}
+					return vector;
+				};
 				break;
 			case SET:
-				for (Vector vector : vectors) {
-					if (axis == 0)
-						vector.setX(deltaValue);
-					else if (axis == 1)
-						vector.setY(deltaValue);
-					else
-						vector.setZ(deltaValue);
-				}
+				double finalDeltaValue = deltaValue;
+				changeFunction = vector -> {
+					if (axis == 0) {
+						vector.setX(finalDeltaValue);
+					} else if (axis == 1) {
+						vector.setY(finalDeltaValue);
+					} else {
+						vector.setZ(finalDeltaValue);
+					}
+					return vector;
+				};
 				break;
 			default:
 				assert false;
 				return;
 		}
-		getExpr().change(event, vectors, ChangeMode.SET);
+
+		//noinspection unchecked,DataFlowIssue
+		((Expression<Vector>) getExpr()).changeInPlace(event, changeFunction);
 	}
 
 	@Override

src/main/java/ch/njol/skript/lang/Expression.java

@@ -35,11 +35,14 @@
 import org.jetbrains.annotations.Nullable;
 import org.skriptlang.skript.lang.converter.Converter;
 
+import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.Iterator;
+import java.util.List;
 import java.util.Map;
 import java.util.Optional;
 import java.util.Spliterators;
+import java.util.function.Function;
 import java.util.stream.Stream;
 import java.util.stream.StreamSupport;
 
@@ -345,6 +348,54 @@ default Map<ChangeMode, Class<?>[]> getAcceptedChangeModes() {
 	 */
 	void change(Event event, @Nullable Object[] delta, ChangeMode mode);
 
+	/**
+	 * Changes the contents of an expression using the given {@link Function}.
+	 * Intended for changes that change properties of the values of the expression, rather than completely
+	 * changing the expression. For example, {@code set vector length of {_v} to 1}, rather than
+	 * {@code set {_v} to vector(0,1,0)}.
+	 * <br>
+	 * This is a 1 to 1 transformation and should not add or remove elements.
+	 * For {@link Variable}s, this will retain indices. For non-{@link Variable}s, it will
+	 * evaluate {@link #getArray(Event)}, apply the change function on each, and call
+	 * {@link #change(Event, Object[], ChangeMode)} with the modified values and {@link ChangeMode#SET}.
+	 *
+	 * @param event The event to use for local variables and evaluation
+	 * @param changeFunction A 1-to-1 function that transforms a single input to a single output.
+	 * @param <R> The output type of the change function. Must be a type returned
+	 *              by {{@link #acceptChange(ChangeMode)}} for {@link ChangeMode#SET}.
+	 */
+	default <R> void changeInPlace(Event event, Function<T, R> changeFunction) {
+		changeInPlace(event, changeFunction, false);
+	}
+
+	/**
+	 * Changes the contents of an expression using the given {@link Function}.
+	 * Intended for changes that change properties of the values of the expression, rather than completely
+	 * changing the expression. For example, {@code set vector length of {_v} to 1}, rather than
+	 * {@code set {_v} to vector(0,1,0)}.
+	 * <br>
+	 * This is a 1 to 1 transformation and should not add or remove elements.
+	 * For {@link Variable}s, this will retain indices. For non-{@link Variable}s, it will
+	 * evaluate the expression, apply the change function on each value, and call
+	 * {@link #change(Event, Object[], ChangeMode)} with the modified values and {@link ChangeMode#SET}.
+	 *
+	 * @param event The event to use for local variables and evaluation
+	 * @param changeFunction A 1-to-1 function that transforms a single input to a single output.
+	 * @param getAll Whether to evaluate with {@link #getAll(Event)} or {@link #getArray(Event)}.
+	 * @param <R> The output type of the change function. Must be a type returned
+	 *              by {{@link #acceptChange(ChangeMode)}} for {@link ChangeMode#SET}.
+	 */
+	default <R> void changeInPlace(Event event, Function<T, R> changeFunction, boolean getAll) {
+		T[] values = getAll ? getAll(event) : getArray(event);
+		if (values.length == 0)
+			return;
+		List<R> newValues = new ArrayList<>();
+		for (T value : values) {
+			newValues.add(changeFunction.apply(value));
+		}
+		change(event, newValues.toArray(), ChangeMode.SET);
+	}
+
 	/**
 	 * This method is called before this expression is set to another one.
 	 * The return value is what will be used for change. You can use modified