From 182b2fc6150b90542371a1824afec691d2f83051 Mon Sep 17 00:00:00 2001
From: Omer Katz <omer.drow@gmail.com>
Date: Fri, 19 Jul 2019 10:07:22 +0300
Subject: [PATCH] Add empty() to PySet and PyFrozenSet.

---
 src/types/set.rs | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/src/types/set.rs b/src/types/set.rs
index 43d9b39d..eaa4311c 100644
--- a/src/types/set.rs
+++ b/src/types/set.rs
@@ -8,6 +8,7 @@ use crate::object::PyObject;
 use crate::AsPyPointer;
 use crate::Python;
 use crate::{ToBorrowedObject, ToPyObject};
+use std::ptr;
 use std::{collections, hash};
 
 /// Represents a Python `set`
@@ -28,6 +29,11 @@ impl PySet {
         unsafe { py.from_owned_ptr_or_err(ffi::PySet_New(list.as_ptr())) }
     }
 
+    /// Creates a new empty set
+    pub fn empty<'p>(py: Python<'p>) -> PyResult<&'p PySet> {
+        unsafe { py.from_owned_ptr_or_err(ffi::PySet_New(ptr::null_mut())) }
+    }
+
     /// Remove all elements from the set.
     #[inline]
     pub fn clear(&self) {
@@ -128,6 +134,11 @@ impl PyFrozenSet {
         unsafe { py.from_owned_ptr_or_err(ffi::PyFrozenSet_New(list.as_ptr())) }
     }
 
+    /// Creates a new empty frozen set
+    pub fn empty<'p>(py: Python<'p>) -> PyResult<&'p PySet> {
+        unsafe { py.from_owned_ptr_or_err(ffi::PyFrozenSet_New(ptr::null_mut())) }
+    }
+
     /// Return the number of items in the set.
     /// This is equivalent to len(p) on a set.
     #[inline]
@@ -177,6 +188,14 @@ mod test {
         assert!(PySet::new(py, &[v]).is_err());
     }
 
+    #[test]
+    fn test_set_empty() {
+        let gil = Python::acquire_gil();
+        let py = gil.python();
+        let set = PySet::empty(py).unwrap();
+        assert_eq!(0, set.len());
+    }
+
     #[test]
     fn test_set_len() {
         let gil = Python::acquire_gil();
@@ -264,6 +283,14 @@ mod test {
         assert!(PyFrozenSet::new(py, &[v]).is_err());
     }
 
+    #[test]
+    fn test_frozenset_empty() {
+        let gil = Python::acquire_gil();
+        let py = gil.python();
+        let set = PyFrozenSet::empty(py).unwrap();
+        assert_eq!(0, set.len());
+    }
+
     #[test]
     fn test_frozenset_contains() {
         let gil = Python::acquire_gil();