It's all virtual

src/lib/Enumerable.vala

@@ -57,31 +57,31 @@ namespace Invercargill {
             return all(i => !predicate(i));
         }
 
-        public Enumerable<T> where(PredicateDelegate<T> predicate) {
+        public virtual Enumerable<T> where(PredicateDelegate<T> predicate) {
             return new FilterQuery<T>(this, predicate);
         }
 
-        public Enumerable<Tout> select<Tout>(TransformDelegate<T, Tout> transform) {
+        public virtual Enumerable<Tout> select<Tout>(TransformDelegate<T, Tout> transform) {
             return new TransformQuery<T, Tout>(this, transform);
         }
 
-        public Enumerable<Tout> select_many<Tout>(TransformDelegate<T, Enumerable<Tout>> transform) {
+        public virtual Enumerable<Tout> select_many<Tout>(TransformDelegate<T, Enumerable<Tout>> transform) {
             return new MergeQuery<Tout>(new TransformQuery<T, Enumerable<Tout>>(this, transform));
         }
 
-        public Enumerable<T> sort(CompareDelegate<T> compare) {
+        public virtual Enumerable<T> sort(CompareDelegate<T> compare) {
             return new SortQuery<T>(this, compare);
         }
 
-        public Enumerable<T> concat(Enumerable<T> other) {
+        public virtual Enumerable<T> concat(Enumerable<T> other) {
             return new ConcatEnumerable<T>(this, other);
         }
 
-        public Enumerable<T> take(int count) {
+        public virtual Enumerable<T> take(int count) {
             return new TakeQuery<T>(this, count);
         }
 
-        public Enumerable<T> skip(int count) {
+        public virtual Enumerable<T> skip(int count) {
             return new SkipQuery<T>(this, count);
         }