Update sparse array

Author: ngallagher

snap-common/src/main/java/org/snapscript/common/SparseArray.java

@@ -2,44 +2,85 @@
 
 public class SparseArray<T> {
 
-   private final Object[][] segments;
-   private final int block;
+   private volatile Object[][] segments;
+   private volatile int capacity;
+   private volatile int block;
 
    public SparseArray(int length) {
       this(length, 32); // compute better default distribution
    }
 
    public SparseArray(int length, int block) {
       this.segments = new Object[length / block + 1][];
+      this.capacity = length;
       this.block = block;
    }
 
-   public void set(int index, T value) {
+   public T set(int index, T value) {
+      int offset = index % block;
+      Object[] segment = segment(index);
+      Object result = segment[offset];
+      
+      segment[offset] = value;
+      return (T)result;
+   }
+   
+   public T get(int index) {
       int section = index /block;
-      Object[] segment = segments[section];
 
-      if(segment == null) {
-         segment = segments[section] = new Object[block];
+      if(section < segments.length) {
+         Object[] segment = segments[section];
+         
+         if(segment != null) {
+            return (T)segment[index % block];
+         }
       }
-      segment[index % block] = value;
+      return null;
    }
 
-   public T get(int index) {
+   public T remove(int index) {
       int section = index /block;
-      Object[] segment = segments[section];
 
-      if(segment != null) {
-         return (T)segment[index % block];
+      if(section < segments.length) {
+         Object[] segment = segments[section];
+         
+         if(segment != null) {
+            int offset = index % block;
+            Object result = segment[offset];
+           
+            segment[offset] = null;
+            return (T)result;
+         }
       }
       return null;
    }
 
-   public void remove(int index) {
+   protected Object[] segment(int index) {
       int section = index /block;
+      
+      if(index >= capacity) {
+         expand(capacity * 2 < index ? index : capacity *2);
+      }
       Object[] segment = segments[section];
 
-      if(segment != null) {
-         segment[index % block] = null;
+      if(segment == null) {
+         segments[section] = new Object[block];
       }
+      return segments[section];
+   }
+   
+   protected void expand(int length) {
+      Object[][] copy = new Object[length / block + 1][];
+
+      for(int i = 0; i < segments.length; i++) {
+         copy[i] = segments[i];
+      }
+      capacity = length;
+      segments = copy;
+   }
+   
+   public int length() {
+      return capacity;
    }
 }
+

snap-tree/src/main/java/org/snapscript/tree/define/TraitConstant.java

@@ -55,6 +55,7 @@ public Initializer compile(Initializer initializer, Type type) throws Exception
       String name = value.getString();
 
       if(!checker.isConstant()) {
+         throw new InternalStateException("Variable '" + name + "' for '" + type + "' must be constant");
       }
       Accessor accessor = new StaticAccessor(initializer, scope, type, name);
       Property property = new AccessorProperty(name, type, constraint, accessor, ModifierType.STATIC.mask | ModifierType.CONSTANT.mask);