Add reversed iterator type.

vm/src/builtins/enumerate.rs

@@ -1,14 +1,15 @@
 use crate::common::lock::PyRwLock;
 
+use crossbeam_utils::atomic::AtomicCell;
 use num_bigint::BigInt;
 use num_traits::Zero;
 
 use super::int::PyIntRef;
 use super::pytype::PyTypeRef;
 use crate::function::OptionalArg;
-use crate::iterator;
 use crate::slots::PyIter;
 use crate::vm::VirtualMachine;
+use crate::{iterator, ItemProtocol, TypeProtocol};
 use crate::{IntoPyObject, PyClassImpl, PyContext, PyObjectRef, PyRef, PyResult, PyValue};
 
 #[pyclass(module = false, name = "enumerate")]
@@ -60,6 +61,52 @@ impl PyIter for PyEnumerate {
     }
 }
 
+#[pyclass(module = false, name = "reversed")]
+#[derive(Debug)]
+pub struct PyReverseSequenceIterator {
+    pub position: AtomicCell<isize>,
+    pub obj: PyObjectRef,
+}
+
+impl PyValue for PyReverseSequenceIterator {
+    fn class(vm: &VirtualMachine) -> &PyTypeRef {
+        &vm.ctx.types.reverse_iter_type
+    }
+}
+
+#[pyimpl(with(PyIter))]
+impl PyReverseSequenceIterator {
+    pub fn new(obj: PyObjectRef, len: isize) -> Self {
+        Self {
+            position: AtomicCell::new(len - 1),
+            obj,
+        }
+    }
+
+    #[pymethod(magic)]
+    fn length_hint(&self) -> PyResult<isize> {
+        Ok(self.position.load() + 1)
+    }
+}
+
+impl PyIter for PyReverseSequenceIterator {
+    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+        let pos = zelf.position.fetch_sub(1);
+        if pos >= 0 {
+            match zelf.obj.get_item(pos, vm) {
+                Err(ref e) if e.isinstance(&vm.ctx.exceptions.index_error) => {
+                    Err(vm.new_stop_iteration())
+                }
+                // also catches stop_iteration => stop_iteration
+                ret => ret,
+            }
+        } else {
+            Err(vm.new_stop_iteration())
+        }
+    }
+}
+
 pub fn init(context: &PyContext) {
     PyEnumerate::extend_class(context, &context.types.enumerate_type);
+    PyReverseSequenceIterator::extend_class(context, &context.types.reverse_iter_type);
 }

vm/src/builtins/iter.rs

@@ -21,12 +21,11 @@ pub enum IterStatus {
     Exhausted,
 }
 
-#[pyclass(module = false, name = "iter")]
+#[pyclass(module = false, name = "iterator")]
 #[derive(Debug)]
 pub struct PySequenceIterator {
     pub position: AtomicCell<isize>,
     pub obj: PyObjectRef,
-    pub reversed: bool,
 }
 
 impl PyValue for PySequenceIterator {
@@ -41,45 +40,26 @@ impl PySequenceIterator {
         Self {
             position: AtomicCell::new(0),
             obj,
-            reversed: false,
-        }
-    }
-
-    pub fn new_reversed(obj: PyObjectRef, len: isize) -> Self {
-        Self {
-            position: AtomicCell::new(len - 1),
-            obj,
-            reversed: true,
         }
     }
 
     #[pymethod(magic)]
     fn length_hint(&self, vm: &VirtualMachine) -> PyResult<isize> {
         let pos = self.position.load();
-        let hint = if self.reversed {
-            pos + 1
-        } else {
-            let len = vm.obj_len(&self.obj)?;
-            len as isize - pos
-        };
-        Ok(hint)
+        let len = vm.obj_len(&self.obj)?;
+        Ok(len as isize - pos)
     }
 }
 
 impl PyIter for PySequenceIterator {
     fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
-        let step: isize = if zelf.reversed { -1 } else { 1 };
-        let pos = zelf.position.fetch_add(step);
-        if pos >= 0 {
-            match zelf.obj.get_item(pos, vm) {
-                Err(ref e) if e.isinstance(&vm.ctx.exceptions.index_error) => {
-                    Err(vm.new_stop_iteration())
-                }
-                // also catches stop_iteration => stop_iteration
-                ret => ret,
+        let pos = zelf.position.fetch_add(1);
+        match zelf.obj.get_item(pos, vm) {
+            Err(ref e) if e.isinstance(&vm.ctx.exceptions.index_error) => {
+                Err(vm.new_stop_iteration())
             }
-        } else {
-            Err(vm.new_stop_iteration())
+            // also catches stop_iteration => stop_iteration
+            ret => ret,
         }
     }
 }

vm/src/builtins/make_module.rs

@@ -12,9 +12,10 @@ mod decl {
     use crate::builtins::bytes::PyBytesRef;
     use crate::builtins::code::PyCodeRef;
     use crate::builtins::dict::PyDictRef;
+    use crate::builtins::enumerate::PyReverseSequenceIterator;
     use crate::builtins::function::{PyCellRef, PyFunctionRef};
     use crate::builtins::int::PyIntRef;
-    use crate::builtins::iter::{PyCallableIterator, PySequenceIterator};
+    use crate::builtins::iter::PyCallableIterator;
     use crate::builtins::list::{PyList, SortOptions};
     use crate::builtins::pybool::IntoPyBool;
     use crate::builtins::pystr::{PyStr, PyStrRef};
@@ -720,7 +721,7 @@ mod decl {
                 "argument to reversed() must be a sequence".to_owned()
             })?;
             let len = vm.obj_len(&obj)? as isize;
-            let obj_iterator = PySequenceIterator::new_reversed(obj, len);
+            let obj_iterator = PyReverseSequenceIterator::new(obj, len);
             Ok(obj_iterator.into_object(vm))
         }
     }

vm/src/types.rs

@@ -68,6 +68,7 @@ pub struct TypeZoo {
     pub generator_type: PyTypeRef,
     pub int_type: PyTypeRef,
     pub iter_type: PyTypeRef,
+    pub reverse_iter_type: PyTypeRef,
     pub complex_type: PyTypeRef,
     pub list_type: PyTypeRef,
     pub list_iterator_type: PyTypeRef,
@@ -182,6 +183,7 @@ impl TypeZoo {
             generator_type: generator::PyGenerator::init_bare_type().clone(),
             getset_type: getset::PyGetSet::init_bare_type().clone(),
             iter_type: iter::PySequenceIterator::init_bare_type().clone(),
+            reverse_iter_type: enumerate::PyReverseSequenceIterator::init_bare_type().clone(),
             list_iterator_type: list::PyListIterator::init_bare_type().clone(),
             list_reverseiterator_type: list::PyListReverseIterator::init_bare_type().clone(),
             mappingproxy_type: mappingproxy::PyMappingProxy::init_bare_type().clone(),