pipeline: Add `NullSkipper`.

Signed-off-by: Jean-Christophe Beaupré <jcbrinfo@users.noreply.github.com>

diff --git a/lib/pipeline.nit b/lib/pipeline.nit
index be553ad..0ca08b2 100644 (file)
--- a/lib/pipeline.nit
+++ b/lib/pipeline.nit
@@ -159,6 +159,45 @@ redef interface Iterator[E]
        end
 end
 
+# Wraps an iterator to skip nulls.
+#
+# ~~~nit
+# var i: Iterator[Int]
+#
+# i = new NullSkipper[Int]([null, 1, null, 2, null: nullable Int].iterator)
+# assert i.to_a == [1, 2]
+#
+# i = new NullSkipper[Int]([1, null, 2, 3: nullable Int].iterator)
+# assert i.to_a == [1, 2, 3]
+# ~~~
+class NullSkipper[E: Object]
+       super Iterator[E]
+
+       # The inner iterator.
+       var inner: Iterator[nullable E]
+
+       redef fun finish do inner.finish
+
+       redef fun is_ok do
+               skip_nulls
+               return inner.is_ok
+       end
+
+       redef fun item do
+               skip_nulls
+               return inner.item.as(E)
+       end
+
+       redef fun next do
+               inner.next
+               skip_nulls
+       end
+
+       private fun skip_nulls do
+               while inner.is_ok and inner.item == null do inner.next
+       end
+end
+
 # Interface that reify a function.
 # Concrete subclasses must implements the `apply` method.
 #