Delay instantiation of cachedValues to save memory

pkl-core/src/main/java/org/pkl/core/runtime/VmDynamic.java

@@ -75,8 +75,7 @@ public boolean isSequence() {
   @Override
   @TruffleBoundary
   public PObject export() {
-    var properties =
-        CollectionUtils.<String, Object>newLinkedHashMap(EconomicMaps.size(cachedValues));
+    var properties = CollectionUtils.<String, Object>newLinkedHashMap(getCacheSize());
 
     iterateMemberValues(
         (key, member, value) -> {
@@ -107,7 +106,9 @@ public boolean equals(Object obj) {
     force(false);
     other.force(false);
     if (getRegularMemberCount() != other.getRegularMemberCount()) return false;
+    if (getCacheSize() == 0) return true;
 
+    assert cachedValues != null;
     var cursor = cachedValues.getEntries();
     while (cursor.advance()) {
       Object key = cursor.getKey();
@@ -129,6 +130,10 @@ public int hashCode() {
 
     force(false);
     var result = 0;
+    if (getCacheSize() == 0) {
+      return 0;
+    }
+    assert cachedValues != null;
     var cursor = cachedValues.getEntries();
 
     while (cursor.advance()) {
@@ -149,8 +154,11 @@ public int getRegularMemberCount() {
     if (cachedRegularMemberCount != -1) return cachedRegularMemberCount;
 
     var result = 0;
-    for (var key : cachedValues.getKeys()) {
-      if (!isHiddenOrLocalProperty(key)) result += 1;
+    if (getCacheSize() != 0) {
+      assert cachedValues != null;
+      for (var key : cachedValues.getKeys()) {
+        if (!isHiddenOrLocalProperty(key)) result += 1;
+      }
     }
     cachedRegularMemberCount = result;
     return result;

pkl-core/src/main/java/org/pkl/core/runtime/VmFunction.java

@@ -106,6 +106,11 @@ public UnmodifiableEconomicMap<Object, ObjectMember> getMembers() {
     return EconomicMaps.create();
   }
 
+  @Override
+  public int getCacheSize() {
+    return 0;
+  }
+
   @Override
   public @Nullable Object getCachedValue(Object key) {
     return null;

pkl-core/src/main/java/org/pkl/core/runtime/VmListing.java

@@ -94,7 +94,7 @@ public VmClass getVmClass() {
   @Override
   @TruffleBoundary
   public List<Object> export() {
-    var properties = new ArrayList<>(EconomicMaps.size(cachedValues));
+    var properties = new ArrayList<>(getCacheSize());
 
     iterateMemberValues(
         (key, prop, value) -> {

pkl-core/src/main/java/org/pkl/core/runtime/VmListingOrMapping.java

@@ -103,6 +103,9 @@ public boolean hasCachedValue(Object key) {
     var objectMember = findMember(key);
     var ret = typecastObjectMember(objectMember, memberValue, IndirectCallNode.getUncached());
     if (ret != memberValue) {
+      if (cachedValues == null) {
+        cachedValues = EconomicMaps.create();
+      }
       EconomicMaps.put(cachedValues, key, ret);
     } else {
       // optimization: don't add to own cached values if typecast results in the same value

pkl-core/src/main/java/org/pkl/core/runtime/VmMapping.java

@@ -104,7 +104,7 @@ public VmSet getAllKeys() {
   @Override
   @TruffleBoundary
   public Map<Object, Object> export() {
-    var properties = CollectionUtils.newLinkedHashMap(EconomicMaps.size(cachedValues));
+    var properties = CollectionUtils.newLinkedHashMap(getCacheSize());
 
     iterateMemberValues(
         (key, prop, value) -> {

pkl-core/src/main/java/org/pkl/core/runtime/VmObject.java

@@ -31,31 +31,23 @@
 public abstract class VmObject extends VmObjectLike {
   @CompilationFinal protected @Nullable VmObject parent;
   protected final UnmodifiableEconomicMap<Object, ObjectMember> members;
-  protected final EconomicMap<Object, Object> cachedValues;
+  protected @Nullable EconomicMap<Object, Object> cachedValues;
 
   protected int cachedHash;
   private boolean forced;
 
   public VmObject(
       MaterializedFrame enclosingFrame,
       @Nullable VmObject parent,
-      UnmodifiableEconomicMap<Object, ObjectMember> members,
-      EconomicMap<Object, Object> cachedValues) {
+      UnmodifiableEconomicMap<Object, ObjectMember> members) {
     super(enclosingFrame);
     this.parent = parent;
     this.members = members;
-    this.cachedValues = cachedValues;
+    this.cachedValues = null;
 
     assert parent != this;
   }
 
-  public VmObject(
-      MaterializedFrame enclosingFrame,
-      @Nullable VmObject parent,
-      UnmodifiableEconomicMap<Object, ObjectMember> members) {
-    this(enclosingFrame, parent, members, EconomicMaps.create());
-  }
-
   public final void lateInitParent(VmObject parent) {
     assert this.parent == null;
     this.parent = parent;
@@ -81,18 +73,32 @@ public final UnmodifiableEconomicMap<Object, ObjectMember> getMembers() {
     return members;
   }
 
+  @Override
+  public int getCacheSize() {
+    return cachedValues == null ? 0 : cachedValues.size();
+  }
+
   @Override
   public @Nullable Object getCachedValue(Object key) {
+    if (cachedValues == null) {
+      return null;
+    }
     return EconomicMaps.get(cachedValues, key);
   }
 
   @Override
   public void setCachedValue(Object key, Object value, ObjectMember objectMember) {
+    if (cachedValues == null) {
+      cachedValues = EconomicMaps.create();
+    }
     EconomicMaps.put(cachedValues, key, value);
   }
 
   @Override
   public boolean hasCachedValue(Object key) {
+    if (cachedValues == null) {
+      return false;
+    }
     return EconomicMaps.containsKey(cachedValues, key);
   }
 
@@ -208,7 +214,7 @@ public final String toString() {
    */
   @TruffleBoundary
   protected final Map<String, Object> exportMembers() {
-    var result = CollectionUtils.<String, Object>newLinkedHashMap(EconomicMaps.size(cachedValues));
+    var result = CollectionUtils.<String, Object>newLinkedHashMap(getCacheSize());
 
     iterateMemberValues(
         (key, member, value) -> {

pkl-core/src/main/java/org/pkl/core/runtime/VmObjectLike.java

@@ -82,6 +82,12 @@ public boolean isModuleObject() {
   /** Returns the declared members of this object. */
   public abstract UnmodifiableEconomicMap<Object, ObjectMember> getMembers();
 
+  /**
+   * @return The (current) size of the properties cache for this object.
+   */
+  @TruffleBoundary
+  public abstract @Nullable int getCacheSize();
+
   /**
    * Reads from the properties cache for this object. The cache contains the values of all members
    * defined in this object or an ancestor thereof which have been requested with this object as the