Rename nbt method to remove confusion about the object being mutable or not

src/main/java/net/minestom/server/chat/ChatHoverEvent.java

@@ -93,7 +93,7 @@ public class ChatHoverEvent {
         JsonObject obj = GsonComponentSerializer.gson().serializer().toJsonTree(Component.empty().hoverEvent(event)).getAsJsonObject();
         obj = obj.get("hoverEvent").getAsJsonObject().get("contents").getAsJsonObject();
 
-        NBTCompound compound = itemStack.getMeta().nbt();
+        NBTCompound compound = itemStack.getMeta().toNBT();
         obj.add("tag", new JsonPrimitive(compound.toSNBT()));
 
         return new ChatHoverEvent("show_item", obj);

src/main/java/net/minestom/server/item/ItemMeta.java

@@ -7,6 +7,7 @@ import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 import org.jglrxavpok.hephaistos.nbt.NBTCompound;
 
+import java.lang.ref.SoftReference;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
@@ -28,6 +29,8 @@ public class ItemMeta {
     private final NBTCompound nbt;
     private final ItemMetaBuilder emptyBuilder;
 
+    private SoftReference<NBTCompound> nbtCache;
+
     protected ItemMeta(@NotNull ItemMetaBuilder metaBuilder) {
         this.damage = metaBuilder.damage;
         this.unbreakable = metaBuilder.unbreakable;
@@ -92,18 +95,23 @@ public class ItemMeta {
     public <T> T getOrDefault(@NotNull ItemTag<T> tag, @Nullable T defaultValue) {
         var key = tag.getKey();
         if (nbt.containsKey(key)) {
-            return tag.read(nbt);
+            return tag.read(toNBT());
         } else {
             return defaultValue;
         }
     }
 
     public <T> @Nullable T get(@NotNull ItemTag<T> tag) {
-        return tag.read(nbt);
+        return tag.read(toNBT());
     }
 
-    public @NotNull NBTCompound nbt() {
-        return nbt;
+    public @NotNull NBTCompound toNBT() {
+        NBTCompound cache = nbtCache.get();
+        if (cache == null) {
+            cache = nbt.deepClone();
+            nbtCache = new SoftReference<>(cache);
+        }
+        return cache;
     }
 
     @Override
@@ -112,7 +120,7 @@ public class ItemMeta {
         if (o == null || getClass() != o.getClass()) return false;
 
         ItemMeta itemMeta = (ItemMeta) o;
-        return nbt.equals(itemMeta.nbt());
+        return nbt.equals(itemMeta.nbt);
     }
 
     @Override

src/main/java/net/minestom/server/item/metadata/CrossbowMeta.java

@@ -193,7 +193,7 @@ public class CrossbowMeta extends ItemMeta {
 
     @NotNull
     private NBTCompound getItemCompound(@NotNull ItemStack itemStack) {
-        NBTCompound compound = itemStack.getMeta().nbt();
+        NBTCompound compound = itemStack.getMeta().toNBT();
         compound.setByte("Count", (byte) itemStack.getAmount());
         compound.setString("id", itemStack.getMaterial().getName());
         return compound;

src/main/java/net/minestom/server/utils/NBTUtils.java

@@ -88,7 +88,7 @@ public final class NBTUtils {
             final ItemStack stack = inventory.getItemStack(i);
             NBTCompound nbt = new NBTCompound();
 
-            NBTCompound tag = stack.getMeta().nbt();
+            NBTCompound tag = stack.getMeta().toNBT();
 
             nbt.set("tag", tag);
             nbt.setByte("Slot", (byte) i);
@@ -288,7 +288,7 @@ public final class NBTUtils {
             packet.writeVarInt(itemStack.getMaterial().getId());
             packet.writeByte((byte) itemStack.getAmount());
 
-            packet.writeNBT("", itemStack.getMeta().nbt());
+            packet.writeNBT("", itemStack.getMeta().toNBT());
         }
     }
 

src/main/java/net/minestom/server/world/biomes/BiomeParticles.java

@@ -100,7 +100,7 @@ public class BiomeParticles {
         @Override
         public NBTCompound toNbt() {
             //todo test count might be wrong type
-            NBTCompound nbtCompound = item.getMeta().nbt();
+            NBTCompound nbtCompound = item.getMeta().toNBT();
             nbtCompound.setString("type", type);
             return nbtCompound;
         }