Use WE Expressions instead of js evaluation (#2941)

* Implement thread-safe expression evaluation

* Update `{args}` to `plot` automatically

* Stringify more money/balance/price occurrences with EconHandler#format

Bukkit/src/main/java/com/plotsquared/bukkit/util/BukkitEconHandler.java

@@ -36,6 +36,7 @@ import net.milkbowl.vault.economy.Economy;
 import org.bukkit.Bukkit;
 import org.bukkit.OfflinePlayer;
 import org.bukkit.plugin.RegisteredServiceProvider;
+import org.checkerframework.checker.nullness.qual.NonNull;
 
 @Singleton public class BukkitEconHandler extends EconHandler {
 
@@ -84,6 +85,11 @@ import org.bukkit.plugin.RegisteredServiceProvider;
         return plotArea.useEconomy();
     }
 
+    @Override
+    public @NonNull String format(double balance) {
+        return this.econ.format(balance);
+    }
+
     @Override
     public boolean isSupported() {
         return true;

Core/src/main/java/com/plotsquared/core/command/Auto.java

@@ -46,8 +46,8 @@ import com.plotsquared.core.plot.world.PlotAreaManager;
 import com.plotsquared.core.services.plots.AutoService;
 import com.plotsquared.core.util.EconHandler;
 import com.plotsquared.core.util.EventDispatcher;
-import com.plotsquared.core.util.Expression;
 import com.plotsquared.core.util.Permissions;
+import com.plotsquared.core.util.PlotExpression;
 import com.plotsquared.core.util.task.AutoClaimFinishTask;
 import com.plotsquared.core.util.task.RunnableVal;
 import com.plotsquared.core.util.task.TaskManager;
@@ -276,24 +276,24 @@ public class Auto extends SubCommand {
             }
         }
         if (this.econHandler != null && plotarea.useEconomy()) {
-            Expression<Double> costExp = plotarea.getPrices().get("claim");
+            PlotExpression costExp = plotarea.getPrices().get("claim");
-            double cost = costExp.evaluate((double) (Settings.Limit.GLOBAL ?
+            double cost = costExp.evaluate(Settings.Limit.GLOBAL ?
                 player.getPlotCount() :
-                player.getPlotCount(plotarea.getWorldName())));
+                player.getPlotCount(plotarea.getWorldName()));
             cost = (size_x * size_z) * cost;
             if (cost > 0d) {
                 if (!force && this.econHandler.getMoney(player) < cost) {
                     player.sendMessage(
                             TranslatableCaption.of("economy.cannot_afford_plot"),
-                            Template.of("money", String.valueOf(cost)),
+                            Template.of("money", this.econHandler.format(cost)),
-                            Template.of("balance", String.valueOf(this.econHandler.getMoney(player)))
+                            Template.of("balance", this.econHandler.format(this.econHandler.getMoney(player)))
                     );
                     return true;
                 }
                 this.econHandler.withdrawMoney(player, cost);
                 player.sendMessage(
                         TranslatableCaption.of("economy.removed_balance"),
-                        Template.of("money", String.valueOf(cost))
+                        Template.of("money", this.econHandler.format(cost))
                 );
             }
         }

Core/src/main/java/com/plotsquared/core/command/Buy.java

@@ -92,15 +92,15 @@ public class Buy extends Command {
         }
         checkTrue(this.econHandler.getMoney(player) >= price,
                 TranslatableCaption.of("economy.cannot_afford_plot"),
-                Template.of("money", String.valueOf(price)),
+                Template.of("money", this.econHandler.format(price)),
-                Template.of("balance", String.valueOf(this.econHandler.getMoney(player))));
+                Template.of("balance", this.econHandler.format(this.econHandler.getMoney(player))));
         this.econHandler.withdrawMoney(player, price);
         // Failure
         // Success
         confirm.run(this, () -> {
             player.sendMessage(
                     TranslatableCaption.of("economy.removed_balance"),
-                    Template.of("money", String.valueOf(price))
+                    Template.of("money", this.econHandler.format(price))
             );
 
             this.econHandler.depositMoney(PlotSquared.platform().playerManager().getOfflinePlayer(plot.getOwnerAbs()), price);
@@ -111,7 +111,7 @@ public class Buy extends Command {
                         TranslatableCaption.of("economy.plot_sold"),
                         Template.of("plot", plot.getId().toString()),
                         Template.of("player", player.getName()),
-                        Template.of("price", String.valueOf(price))
+                        Template.of("price", this.econHandler.format(price))
                 );
             }
             PlotFlag<?, ?> plotFlag = plot.getFlagContainer().getFlag(PriceFlag.class);

Core/src/main/java/com/plotsquared/core/command/Claim.java

@@ -42,8 +42,8 @@ import com.plotsquared.core.plot.Plot;
 import com.plotsquared.core.plot.PlotArea;
 import com.plotsquared.core.util.EconHandler;
 import com.plotsquared.core.util.EventDispatcher;
-import com.plotsquared.core.util.Expression;
 import com.plotsquared.core.util.Permissions;
+import com.plotsquared.core.util.PlotExpression;
 import com.plotsquared.core.util.task.TaskManager;
 import net.kyori.adventure.text.minimessage.Template;
 import org.slf4j.Logger;
@@ -136,20 +136,22 @@ public class Claim extends SubCommand {
             }
         }
         if (this.econHandler.isEnabled(area) && !force) {
-            Expression<Double> costExr = area.getPrices().get("claim");
+            PlotExpression costExr = area.getPrices().get("claim");
-            double cost = costExr.evaluate((double) currentPlots);
+            double cost = costExr.evaluate(currentPlots);
             if (cost > 0d) {
                 if (this.econHandler.getMoney(player) < cost) {
                     player.sendMessage(
                             TranslatableCaption.of("economy.cannot_afford_plot"),
-                            Template.of("money", String.valueOf(cost))
+                            Template.of("money", this.econHandler.format(cost)),
+                            Template.of("balance", this.econHandler.format(this.econHandler.getMoney(player)))
                     );
+                    return false;
                 }
                 this.econHandler.withdrawMoney(player, cost);
                 player.sendMessage(
                         TranslatableCaption.of("economy.removed_balance"),
-                        Template.of("money", String.valueOf(cost)),
+                        Template.of("money", this.econHandler.format(cost)),
-                        Template.of("balance", String.valueOf(this.econHandler.getMoney(player)))
+                        Template.of("balance", this.econHandler.format(this.econHandler.getMoney(player)))
                 );
             }
         }

Core/src/main/java/com/plotsquared/core/command/Delete.java

@@ -26,24 +26,23 @@
 package com.plotsquared.core.command;
 
 import com.google.inject.Inject;
-import com.plotsquared.core.events.TeleportCause;
-import com.plotsquared.core.permissions.Permission;
 import com.plotsquared.core.configuration.Settings;
 import com.plotsquared.core.configuration.caption.TranslatableCaption;
 import com.plotsquared.core.events.Result;
+import com.plotsquared.core.events.TeleportCause;
 import com.plotsquared.core.location.Location;
+import com.plotsquared.core.permissions.Permission;
 import com.plotsquared.core.player.PlotPlayer;
 import com.plotsquared.core.plot.Plot;
 import com.plotsquared.core.plot.PlotArea;
 import com.plotsquared.core.util.EconHandler;
 import com.plotsquared.core.util.EventDispatcher;
-import com.plotsquared.core.util.Expression;
 import com.plotsquared.core.util.Permissions;
+import com.plotsquared.core.util.PlotExpression;
 import com.plotsquared.core.util.task.TaskManager;
 import net.kyori.adventure.text.minimessage.Template;
 
 import javax.annotation.Nonnull;
-import javax.annotation.Nullable;
 
 
 @CommandDeclaration(command = "delete",
@@ -106,13 +105,13 @@ public class Delete extends SubCommand {
             boolean result = plot.getPlotModificationManager().deletePlot(player, () -> {
                 plot.removeRunning();
                 if (this.econHandler.isEnabled(plotArea)) {
-                    Expression<Double> valueExr = plotArea.getPrices().get("sell");
+                    PlotExpression valueExr = plotArea.getPrices().get("sell");
-                    double value = plots.size() * valueExr.evaluate((double) currentPlots);
+                    double value = plots.size() * valueExr.evaluate(currentPlots);
                     if (value > 0d) {
                         this.econHandler.depositMoney(player, value);
                         player.sendMessage(
                                 TranslatableCaption.of("economy.added_balance"),
-                                Template.of("money", String.valueOf(value))
+                                Template.of("money", this.econHandler.format(value))
                         );
                     }
                 }

Core/src/main/java/com/plotsquared/core/command/MainCommand.java

@@ -27,10 +27,10 @@ package com.plotsquared.core.command;
 
 import com.google.inject.Injector;
 import com.plotsquared.core.PlotSquared;
-import com.plotsquared.core.permissions.Permission;
 import com.plotsquared.core.configuration.Settings;
 import com.plotsquared.core.configuration.caption.TranslatableCaption;
 import com.plotsquared.core.location.Location;
+import com.plotsquared.core.permissions.Permission;
 import com.plotsquared.core.player.ConsolePlayer;
 import com.plotsquared.core.player.MetaDataAccess;
 import com.plotsquared.core.player.PlayerMetaDataKeys;
@@ -38,8 +38,8 @@ import com.plotsquared.core.player.PlotPlayer;
 import com.plotsquared.core.plot.Plot;
 import com.plotsquared.core.plot.PlotArea;
 import com.plotsquared.core.util.EconHandler;
-import com.plotsquared.core.util.Expression;
 import com.plotsquared.core.util.Permissions;
+import com.plotsquared.core.util.PlotExpression;
 import com.plotsquared.core.util.task.RunnableVal2;
 import com.plotsquared.core.util.task.RunnableVal3;
 import org.slf4j.Logger;
@@ -190,11 +190,10 @@ public class MainCommand extends Command {
                         CmdConfirm.addPending(player, cmd.getUsage(), () -> {
                             PlotArea area = player.getApplicablePlotArea();
                             if (area != null && econHandler.isEnabled(area)) {
-                                Expression<Double> priceEval =
+                                PlotExpression priceEval =
                                     area.getPrices().get(cmd.getFullId());
-                                Double price = priceEval != null ? priceEval.evaluate(0d) : 0d;
+                                double price = priceEval != null ? priceEval.evaluate(0d) : 0d;
-                                if (price != null
+                                if (econHandler.getMoney(player) < price) {
-                                    && econHandler.getMoney(player) < price) {
                                     if (failure != null) {
                                         failure.run();
                                     }
@@ -207,11 +206,10 @@ public class MainCommand extends Command {
                         });
                         return;
                     }
-                    if (econHandler != null) {
                     PlotArea area = player.getApplicablePlotArea();
-                        if (area != null) {
+                    if (area != null && econHandler.isEnabled(area)) {
-                            Expression<Double> priceEval = area.getPrices().get(cmd.getFullId());
+                        PlotExpression priceEval = area.getPrices().get(cmd.getFullId());
-                            Double price = priceEval != null ? priceEval.evaluate(0d) : 0d;
+                        double price = priceEval != null ? priceEval.evaluate(0d) : 0d;
                         if (price != 0d && econHandler.getMoney(player) < price) {
                             if (failure != null) {
                                 failure.run();
@@ -219,7 +217,6 @@ public class MainCommand extends Command {
                             return;
                         }
                     }
-                    }
                     if (success != null) {
                         success.run();
                     }
@@ -277,12 +274,10 @@ public class MainCommand extends Command {
                 if ("f".equals(args[0].substring(1))) {
                     confirm = new RunnableVal3<Command, Runnable, Runnable>() {
                         @Override public void run(Command cmd, Runnable success, Runnable failure) {
-                            if (PlotSquared.platform().econHandler() != null) {
+                            if (area != null && PlotSquared.platform().econHandler().isEnabled(area)) {
-                                PlotArea area = player.getApplicablePlotArea();
+                                PlotExpression priceEval =
-                                if (area != null) {
-                                    Expression<Double> priceEval =
                                     area.getPrices().get(cmd.getFullId());
-                                    Double price = priceEval != null ? priceEval.evaluate(0d) : 0d;
+                                double price = priceEval != null ? priceEval.evaluate(0d) : 0d;
                                 if (price != 0d
                                     && PlotSquared.platform().econHandler().getMoney(player) < price) {
                                     if (failure != null) {
@@ -291,7 +286,6 @@ public class MainCommand extends Command {
                                     return;
                                 }
                             }
-                            }
                             if (success != null) {
                                 success.run();
                             }

Core/src/main/java/com/plotsquared/core/command/Merge.java

@@ -39,8 +39,8 @@ import com.plotsquared.core.plot.Plot;
 import com.plotsquared.core.plot.PlotArea;
 import com.plotsquared.core.util.EconHandler;
 import com.plotsquared.core.util.EventDispatcher;
-import com.plotsquared.core.util.Expression;
 import com.plotsquared.core.util.Permissions;
+import com.plotsquared.core.util.PlotExpression;
 import com.plotsquared.core.util.StringMan;
 import net.kyori.adventure.text.minimessage.Template;
 
@@ -162,8 +162,8 @@ public class Merge extends SubCommand {
             return false;
         }
         final PlotArea plotArea = plot.getArea();
-        Expression<Double> priceExr = plotArea.getPrices().getOrDefault("merge", null);
+        PlotExpression priceExr = plotArea.getPrices().getOrDefault("merge", null);
-        final double price = priceExr == null ? 0d : priceExr.evaluate((double) size);
+        final double price = priceExr == null ? 0d : priceExr.evaluate(size);
 
         UUID uuid = player.getUUID();
         if (direction == Direction.ALL) {
@@ -184,7 +184,8 @@ public class Merge extends SubCommand {
                     this.econHandler.withdrawMoney(player, price);
                     player.sendMessage(
                             TranslatableCaption.of("economy.removed_balance"),
-                            Template.of("money", String.valueOf(price))
+                            Template.of("money", this.econHandler.format(price)),
+                            Template.of("balance", this.econHandler.format(this.econHandler.getMoney(player)))
                     );
                 }
                 player.sendMessage(TranslatableCaption.of("merge.success_merge"));
@@ -205,7 +206,7 @@ public class Merge extends SubCommand {
             && this.econHandler.getMoney(player) < price) {
             player.sendMessage(
                     TranslatableCaption.of("economy.cannot_afford_merge"),
-                    Template.of("money", String.valueOf(price))
+                    Template.of("money", this.econHandler.format(price))
             );
             return false;
         }
@@ -228,7 +229,7 @@ public class Merge extends SubCommand {
                 this.econHandler.withdrawMoney(player, price);
                 player.sendMessage(
                         TranslatableCaption.of("economy.removed_balance"),
-                        Template.of("money", String.valueOf(price))
+                        Template.of("money", this.econHandler.format(price))
                 );
             }
             player.sendMessage(TranslatableCaption.of("merge.success_merge"));
@@ -268,14 +269,14 @@ public class Merge extends SubCommand {
                     if (!force && this.econHandler.getMoney(player) < price) {
                         player.sendMessage(
                                 TranslatableCaption.of("economy.cannot_afford_merge"),
-                                Template.of("money", String.valueOf(price))
+                                Template.of("money", this.econHandler.format(price))
                         );
                         return;
                     }
                     this.econHandler.withdrawMoney(player, price);
                     player.sendMessage(
                             TranslatableCaption.of("economy.removed_balance"),
-                            Template.of("money", String.valueOf(price))
+                            Template.of("money", this.econHandler.format(price))
                     );
                 }
                 player.sendMessage(TranslatableCaption.of("merge.success_merge"));

Core/src/main/java/com/plotsquared/core/components/ComponentPresetManager.java

@@ -186,7 +186,7 @@ public class ComponentPresetManager {
                     } else {
                         econHandler.withdrawMoney(getPlayer(), componentPreset.getCost());
                         getPlayer().sendMessage(TranslatableCaption.of("economy.removed_balance"),
-                                Template.of("money", componentPreset.getCost() + ""));
+                                Template.of("money", econHandler.format(componentPreset.getCost())));
                     }
                 }
 

Core/src/main/java/com/plotsquared/core/plot/PlotArea.java

@@ -57,8 +57,8 @@ import com.plotsquared.core.plot.flag.implementations.DoneFlag;
 import com.plotsquared.core.plot.flag.types.DoubleFlag;
 import com.plotsquared.core.queue.GlobalBlockQueue;
 import com.plotsquared.core.queue.QueueCoordinator;
-import com.plotsquared.core.util.Expression;
 import com.plotsquared.core.util.MathMan;
+import com.plotsquared.core.util.PlotExpression;
 import com.plotsquared.core.util.RegionUtil;
 import com.plotsquared.core.util.StringMan;
 import com.sk89q.worldedit.math.BlockVector2;
@@ -134,7 +134,7 @@ public abstract class PlotArea {
     private int maxBuildHeight = 256;
     private int minBuildHeight = 1;
     private GameMode gameMode = GameModes.CREATIVE;
-    private Map<String, Expression<Double>> prices = new HashMap<>();
+    private Map<String, PlotExpression> prices = new HashMap<>();
     private List<String> schematics = new ArrayList<>();
     private boolean roadFlags = false;
     private boolean worldBorder = false;
@@ -306,7 +306,12 @@ public abstract class PlotArea {
         if (this.useEconomy) {
             this.prices = new HashMap<>();
             for (String key : priceSection.getKeys(false)) {
-                this.prices.put(key, Expression.doubleExpression(priceSection.getString(key)));
+                String raw = priceSection.getString(key);
+                if (raw.contains("{args}")) {
+                    raw = raw.replace("{args}", "plots");
+                    priceSection.set(key, raw); // update if replaced
+                }
+                this.prices.put(key, PlotExpression.compile(raw, "plots"));
             }
         }
         this.plotChat = config.getBoolean("chat.enabled");
@@ -1315,7 +1320,7 @@ public abstract class PlotArea {
         return this.gameMode;
     }
 
-    public Map<String, Expression<Double>> getPrices() {
+    public Map<String, PlotExpression> getPrices() {
         return this.prices;
     }
 

Core/src/main/java/com/plotsquared/core/util/EconHandler.java

@@ -29,7 +29,7 @@ import com.plotsquared.core.player.ConsolePlayer;
 import com.plotsquared.core.player.OfflinePlotPlayer;
 import com.plotsquared.core.player.PlotPlayer;
 import com.plotsquared.core.plot.PlotArea;
-import com.sk89q.worldedit.EditSession;
+import org.checkerframework.checker.nullness.qual.NonNull;
 
 public abstract class EconHandler {
 
@@ -75,6 +75,14 @@ public abstract class EconHandler {
      */
     public abstract boolean isEnabled(PlotArea plotArea);
 
+    /**
+     * Formats the given balance into a human-readable number.
+     *
+     * @param balance the balance to format.
+     * @return the balance as formatted string.
+     */
+    public abstract @NonNull String format(double balance);
+
     /**
      * Returns whether economy is supported by the server or not.
      *
@@ -114,6 +122,11 @@ public abstract class EconHandler {
             return false;
         }
 
+        @Override
+        public @NonNull String format(double balance) {
+            return "";
+        }
+
         @Override
         public boolean isSupported() {
             return false;

Core/src/main/java/com/plotsquared/core/util/Expression.java

@@ -1,85 +0,0 @@
-/*
- *       _____  _       _    _____                                _
- *      |  __ \| |     | |  / ____|                              | |
- *      | |__) | | ___ | |_| (___   __ _ _   _  __ _ _ __ ___  __| |
- *      |  ___/| |/ _ \| __|\___ \ / _` | | | |/ _` | '__/ _ \/ _` |
- *      | |    | | (_) | |_ ____) | (_| | |_| | (_| | | |  __/ (_| |
- *      |_|    |_|\___/ \__|_____/ \__, |\__,_|\__,_|_|  \___|\__,_|
- *                                    | |
- *                                    |_|
- *            PlotSquared plot management system for Minecraft
- *                  Copyright (C) 2021 IntellectualSites
- *
- *     This program is free software: you can redistribute it and/or modify
- *     it under the terms of the GNU General Public License as published by
- *     the Free Software Foundation, either version 3 of the License, or
- *     (at your option) any later version.
- *
- *     This program is distributed in the hope that it will be useful,
- *     but WITHOUT ANY WARRANTY; without even the implied warranty of
- *     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- *     GNU General Public License for more details.
- *
- *     You should have received a copy of the GNU General Public License
- *     along with this program.  If not, see <https://www.gnu.org/licenses/>.
- */
-package com.plotsquared.core.util;
-
-import com.plotsquared.core.command.DebugExec;
-import com.plotsquared.core.command.MainCommand;
-import com.plotsquared.core.configuration.Settings;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-
-import javax.script.ScriptException;
-
-public abstract class Expression<T> {
-
-    private static final Logger logger = LoggerFactory.getLogger("P2/" + Expression.class.getSimpleName());
-
-    public static <U> Expression<U> constant(final U value) {
-        return new Expression<U>() {
-            @Override public U evaluate(U arg) {
-                return value;
-            }
-        };
-    }
-
-    public static Expression<Double> linearDouble(final Double value) {
-        return new Expression<Double>() {
-            @Override public Double evaluate(Double arg) {
-                return (arg * value);
-            }
-        };
-    }
-
-    public static Expression<Double> doubleExpression(final String expression) {
-        try {
-            return constant(Double.parseDouble(expression));
-        } catch (NumberFormatException ignore) {
-        }
-        if (expression.endsWith("*{arg}")) {
-            try {
-                return linearDouble(
-                    Double.parseDouble(expression.substring(0, expression.length() - 6)));
-            } catch (NumberFormatException ignore) {
-            }
-        }
-        return new Expression<Double>() {
-            @Override public Double evaluate(Double arg) {
-                DebugExec exec = (DebugExec) MainCommand.getInstance().getCommand(DebugExec.class);
-                try {
-                    return (Double) exec.getEngine().eval(expression.replace("{arg}", "" + arg));
-                } catch (ScriptException e) {
-                    if (Settings.DEBUG) {
-                        logger.info("Invalid expression: {}", expression);
-                    }
-                    e.printStackTrace();
-                }
-                return 0d;
-            }
-        };
-    }
-
-    public abstract T evaluate(T arg);
-}

Core/src/main/java/com/plotsquared/core/util/PlotExpression.java

@@ -0,0 +1,70 @@
+/*
+ *       _____  _       _    _____                                _
+ *      |  __ \| |     | |  / ____|                              | |
+ *      | |__) | | ___ | |_| (___   __ _ _   _  __ _ _ __ ___  __| |
+ *      |  ___/| |/ _ \| __|\___ \ / _` | | | |/ _` | '__/ _ \/ _` |
+ *      | |    | | (_) | |_ ____) | (_| | |_| | (_| | | |  __/ (_| |
+ *      |_|    |_|\___/ \__|_____/ \__, |\__,_|\__,_|_|  \___|\__,_|
+ *                                    | |
+ *                                    |_|
+ *            PlotSquared plot management system for Minecraft
+ *                  Copyright (C) 2021 IntellectualSites
+ *
+ *     This program is free software: you can redistribute it and/or modify
+ *     it under the terms of the GNU General Public License as published by
+ *     the Free Software Foundation, either version 3 of the License, or
+ *     (at your option) any later version.
+ *
+ *     This program is distributed in the hope that it will be useful,
+ *     but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *     GNU General Public License for more details.
+ *
+ *     You should have received a copy of the GNU General Public License
+ *     along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+package com.plotsquared.core.util;
+
+import com.sk89q.worldedit.internal.expression.Expression;
+import org.checkerframework.checker.nullness.qual.NonNull;
+
+/**
+ * An expression that can be evaluated.
+ * Evaluation is thread-safe.
+ * This is a wrapper for {@link Expression}.
+ */
+public class PlotExpression {
+    private final Expression expression;
+    private final Object lock = new Object();
+
+    /**
+     * Compiles an expression from a string.
+     *
+     * @param expression    the expression to compile.
+     * @param variableNames the variables that can be set in {@link #evaluate(double...)}.
+     * @return the compiled expression.
+     */
+    public static @NonNull PlotExpression compile(final @NonNull String expression,
+                                                  final @NonNull String @NonNull ... variableNames) {
+        return new PlotExpression(expression, variableNames);
+    }
+
+    private PlotExpression(final @NonNull String rawExpression, final @NonNull String @NonNull [] variableNames) {
+        this.expression = Expression.compile(rawExpression, variableNames);
+    }
+
+    /**
+     * Evaluates the expression with the given variable values.
+     *
+     * @param values the values to set the variables to.
+     * @return the result of the evaluation.
+     */
+    public double evaluate(double... values) {
+        double evaluate;
+        // synchronization is likely the best option in terms of memory and cpu consumption
+        synchronized (this.lock) {
+            evaluate = this.expression.evaluate(values);
+        }
+        return evaluate;
+    }
+}