add method to set length

Author: querolita

src/lib/provable/dynamic-array.ts

@@ -321,6 +321,19 @@ class DynamicArrayBase<ProvableValue = any, Value = any> {
     this.length = oldLength.sub(n).seal();
   }
 
+  /**
+   * Sets the length of the current array to a new value, checking that the
+   * new length is less or equal than the capacity.
+   * 
+   * @param newLength 
+   * 
+   * **Warning**: This does not change (add nor remove) the values of the array.
+   */
+  setLengthTo(n: Field): void {
+    n.assertLessThanOrEqual(new Field(this.capacity));
+    this.length = n;
+  }
+
   /**
    * Push a value, without changing the capacity.
    *