Merge 015666a into ab176ab

ftoolz/adt/ring.py

@@ -0,0 +1,30 @@
+from collections import deque
+from typing import Iterable, Iterator, Sized, TypeVar
+
+from cytoolz.functoolz import do
+
+from ftoolz.typing import Seq
+
+_E = TypeVar('_E')
+
+
+class Ring(Iterator[_E], Sized):  # pylint: disable=E0239
+    """Fixed-size in-memory rotating list of elements"""
+
+    # pylint: disable=W0231
+    def __init__(self, elements: Iterable[_E] = tuple()) -> None:
+        self._ring = deque(elements)
+
+    def __len__(self) -> int:
+        return len(self._ring)
+
+    def __bool__(self) -> bool:
+        return bool(self._ring)
+
+    def __next__(self) -> _E:
+        if not self:
+            raise StopIteration
+        return do(self._ring.append, self._ring.popleft())
+
+    def state(self) -> Seq[_E]:
+        return tuple(self._ring)