diff --git a/README.md b/README.md
index 0f5dda5..952aa5e 100644
--- a/README.md
+++ b/README.md
@@ -11,12 +11,12 @@ flatcontainer = "0.6"
 ## Example
 
 ```rust
-use flatcontainer::{Index, RegionPreference};
+use flatcontainer::{Index, Push, RegionPreference};
 
 let r: Result<_, u16> = Ok("abc");
 let mut c = <<Result<&str, u16> as RegionPreference>::Region>::default();
 c.push(&r);
-assert_eq!(r, c.index(0));
+assert_eq!(Ok("abc"), c.index(0));
 ```
 
 ## Details
diff --git a/src/impls.rs b/src/impls.rs
index 9380937..d0a2c61 100644
--- a/src/impls.rs
+++ b/src/impls.rs
@@ -7,7 +7,7 @@
 // pub mod index;
 // pub mod mirror;
 pub mod option;
-// pub mod result;
+pub mod result;
 pub mod slice;
 pub mod slice_owned;
 pub mod string;
diff --git a/src/impls/result.rs b/src/impls/result.rs
index 99ea871..5e92f5a 100644
--- a/src/impls/result.rs
+++ b/src/impls/result.rs
@@ -3,7 +3,10 @@
 #[cfg(feature = "serde")]
 use serde::{Deserialize, Serialize};
 
-use crate::{IntoOwned, Push, Region, RegionPreference, ReserveItems};
+use crate::rank_select::RankSelect;
+use crate::{
+    Clear, HeapSize, Index, IndexAs, IntoOwned, Len, Push, Region, RegionPreference, ReserveItems,
+};
 
 impl<T: RegionPreference, E: RegionPreference> RegionPreference for Result<T, E> {
     type Owned = Result<T::Owned, E::Owned>;
@@ -16,93 +19,130 @@ impl<T: RegionPreference, E: RegionPreference> RegionPreference for Result<T, E>
 ///
 /// Add results to a result region:
 /// ```
-/// use flatcontainer::{RegionPreference, Push, Region, ResultRegion};
-/// let mut r =
-///     <ResultRegion<<() as RegionPreference>::Region, <String as RegionPreference>::Region>>::default();
+/// use flatcontainer::{RegionPreference, Push, Region, ResultRegion, Index};
+/// let mut r = <Result<(), String> as RegionPreference>::Region::default();
 ///
-/// let ok_index = r.push(Result::<(), String>::Ok(()));
-/// let err_index = r.push(Result::<(), String>::Err("Error".to_string()));
+/// r.push(Result::<(), String>::Ok(()));
+/// r.push(Result::<(), String>::Err("Error".to_string()));
 ///
-/// assert_eq!(Ok(()), r.index(ok_index));
-/// assert_eq!(Err("Error"), r.index(err_index));
+/// assert_eq!(Ok(&()), r.index(0));
+/// assert_eq!(Err("Error"), r.index(1));
 /// ```
 #[derive(Default, Debug)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
-pub struct ResultRegion<T, E> {
+pub struct ResultRegion<T, E, RC = Vec<u64>, RV = Vec<u64>> {
+    ranks: RankSelect<RC, RV>,
     oks: T,
     errs: E,
 }
 
-impl<T: Clone, E: Clone> Clone for ResultRegion<T, E> {
+impl<T: Clone, E: Clone, RC: Clone, RV: Clone> Clone for ResultRegion<T, E, RC, RV> {
     fn clone(&self) -> Self {
         Self {
+            ranks: self.ranks.clone(),
             oks: self.oks.clone(),
             errs: self.errs.clone(),
         }
     }
 
     fn clone_from(&mut self, source: &Self) {
+        self.ranks.clone_from(&source.ranks);
         self.oks.clone_from(&source.oks);
         self.errs.clone_from(&source.errs);
     }
 }
 
-impl<T, E> Region for ResultRegion<T, E>
+impl<T, E, RC, RV> Region for ResultRegion<T, E, RC, RV>
 where
     T: Region,
     E: Region,
+    RC: Region,
+    RV: Region,
 {
-    type Owned = Result<T::Owned, E::Owned>;
-    type ReadItem<'a> = Result<T::ReadItem<'a>, E::ReadItem<'a>> where Self: 'a;
-    type Index = Result<T::Index, E::Index>;
-
     #[inline]
     fn merge_regions<'a>(regions: impl Iterator<Item = &'a Self> + Clone) -> Self
     where
         Self: 'a,
     {
         Self {
+            ranks: RankSelect::merge_regions(regions.clone().map(|r| &r.ranks)),
             oks: T::merge_regions(regions.clone().map(|r| &r.oks)),
             errs: E::merge_regions(regions.map(|r| &r.errs)),
         }
     }
 
-    #[inline]
-    fn index(&self, index: Self::Index) -> Self::ReadItem<'_> {
-        match index {
-            Ok(index) => Ok(self.oks.index(index)),
-            Err(index) => Err(self.errs.index(index)),
-        }
-    }
-
     #[inline]
     fn reserve_regions<'a, I>(&mut self, regions: I)
     where
         Self: 'a,
         I: Iterator<Item = &'a Self> + Clone,
     {
+        self.ranks
+            .reserve_regions(regions.clone().map(|r| &r.ranks));
         self.oks.reserve_regions(regions.clone().map(|r| &r.oks));
         self.errs.reserve_regions(regions.map(|r| &r.errs));
     }
+}
+
+impl<T, E, RC, RV> Index for ResultRegion<T, E, RC, RV>
+where
+    T: Index,
+    E: Index,
+    RC: IndexAs<u64> + Len,
+    RV: IndexAs<u64> + Len,
+{
+    type Owned = Result<T::Owned, E::Owned>;
+    type ReadItem<'a> = Result<T::ReadItem<'a>, E::ReadItem<'a>> where Self: 'a;
+
+    #[inline]
+    fn index(&self, index: usize) -> Self::ReadItem<'_> {
+        if self.ranks.index_as(index) {
+            Ok(self.oks.index(self.ranks.rank(index)))
+        } else {
+            Err(self.errs.index(index - self.ranks.rank(index)))
+        }
+    }
 
+    #[inline]
+    fn reborrow<'b, 'a: 'b>(item: Self::ReadItem<'a>) -> Self::ReadItem<'b>
+    where
+        Self: 'a,
+    {
+        item.map(T::reborrow).map_err(E::reborrow)
+    }
+}
+
+impl<T, E, RC, RV> Clear for ResultRegion<T, E, RC, RV>
+where
+    T: Clear,
+    E: Clear,
+{
     #[inline]
     fn clear(&mut self) {
         self.oks.clear();
         self.errs.clear();
     }
+}
 
+impl<T, E, RC, RV> HeapSize for ResultRegion<T, E, RC, RV>
+where
+    T: HeapSize,
+    E: HeapSize,
+{
     #[inline]
     fn heap_size<F: FnMut(usize, usize)>(&self, mut callback: F) {
         self.oks.heap_size(&mut callback);
         self.errs.heap_size(callback);
     }
+}
 
+impl<T, E, RC, RV> Len for ResultRegion<T, E, RC, RV>
+where
+    RV: Len,
+{
     #[inline]
-    fn reborrow<'b, 'a: 'b>(item: Self::ReadItem<'a>) -> Self::ReadItem<'b>
-    where
-        Self: 'a,
-    {
-        item.map(T::reborrow).map_err(E::reborrow)
+    fn len(&self) -> usize {
+        self.ranks.len()
     }
 }
 
@@ -134,35 +174,51 @@ where
     }
 }
 
-impl<T, TC, E, EC> Push<Result<T, E>> for ResultRegion<TC, EC>
+impl<T, TC, E, EC, RC, RV> Push<Result<T, E>> for ResultRegion<TC, EC, RC, RV>
 where
-    TC: Region + Push<T>,
-    EC: Region + Push<E>,
+    TC: Push<T>,
+    EC: Push<E>,
+    RC: IndexAs<u64> + Len + Push<u64>,
+    RV: IndexAs<u64> + Len + Push<u64>,
 {
     #[inline]
-    fn push(&mut self, item: Result<T, E>) -> <ResultRegion<TC, EC> as Region>::Index {
+    fn push(&mut self, item: Result<T, E>) {
         match item {
-            Ok(t) => Ok(self.oks.push(t)),
-            Err(e) => Err(self.errs.push(e)),
+            Ok(t) => {
+                self.ranks.push(true);
+                self.oks.push(t);
+            }
+            Err(r) => {
+                self.ranks.push(false);
+                self.errs.push(r);
+            }
         }
     }
 }
 
-impl<'a, T: 'a, TC, E: 'a, EC> Push<&'a Result<T, E>> for ResultRegion<TC, EC>
+impl<'a, T: 'a, TC, E: 'a, EC, RC, RV> Push<&'a Result<T, E>> for ResultRegion<TC, EC, RC, RV>
 where
-    TC: Region + Push<&'a T>,
-    EC: Region + Push<&'a E>,
+    TC: Push<&'a T>,
+    EC: Push<&'a E>,
+    RC: IndexAs<u64> + Len + Push<u64>,
+    RV: IndexAs<u64> + Len + Push<u64>,
 {
     #[inline]
-    fn push(&mut self, item: &'a Result<T, E>) -> <ResultRegion<TC, EC> as Region>::Index {
+    fn push(&mut self, item: &'a Result<T, E>) {
         match item {
-            Ok(t) => Ok(self.oks.push(t)),
-            Err(e) => Err(self.errs.push(e)),
+            Ok(t) => {
+                self.ranks.push(true);
+                self.oks.push(t);
+            }
+            Err(r) => {
+                self.ranks.push(false);
+                self.errs.push(r);
+            }
         }
     }
 }
 
-impl<T, TC, E, EC> ReserveItems<Result<T, E>> for ResultRegion<TC, EC>
+impl<T, TC, E, EC, RC, RV> ReserveItems<Result<T, E>> for ResultRegion<TC, EC, RC, RV>
 where
     TC: Region + ReserveItems<T>,
     EC: Region + ReserveItems<E>,
@@ -177,7 +233,8 @@ where
     }
 }
 
-impl<'a, T: 'a, TC, E: 'a, EC> ReserveItems<&'a Result<T, E>> for ResultRegion<TC, EC>
+impl<'a, T: 'a, TC, E: 'a, EC, RC, RV> ReserveItems<&'a Result<T, E>>
+    for ResultRegion<TC, EC, RC, RV>
 where
     TC: Region + ReserveItems<&'a T>,
     EC: Region + ReserveItems<&'a E>,
@@ -196,13 +253,13 @@ where
 
 #[cfg(test)]
 mod tests {
-    use crate::{MirrorRegion, OwnedRegion, Region, ReserveItems};
+    use crate::{OwnedRegion, ReserveItems};
 
     use super::*;
 
     #[test]
     fn test_reserve() {
-        let mut r = <ResultRegion<MirrorRegion<u8>, MirrorRegion<u8>>>::default();
+        let mut r = <ResultRegion<Vec<u8>, Vec<u8>>>::default();
         ReserveItems::reserve_items(&mut r, [Ok(0), Err(1)].iter());
 
         ReserveItems::reserve_items(&mut r, [Ok(0), Err(1)].into_iter());
diff --git a/src/impls/slice.rs b/src/impls/slice.rs
index 4780cb1..1cb49f1 100644
--- a/src/impls/slice.rs
+++ b/src/impls/slice.rs
@@ -50,13 +50,13 @@ type Idx = u64;
 ///     .split(" ")
 ///     .collect::<Vec<_>>();
 ///
-/// r.push(&panagram_en);
 /// r.push(&panagram_de);
+/// r.push(&panagram_en);
 ///
 /// assert!(panagram_de.into_iter().eq(r.index(0)));
 /// assert!(panagram_en.into_iter().eq(r.index(1)));
 ///
-/// assert_eq!(r.index(1).get(2), "jagen");
+/// assert_eq!(r.index(0).get(2), "jagen");
 /// ```
 #[derive(Debug)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
diff --git a/src/lib.rs b/src/lib.rs
index 2c7c738..008b721 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -13,7 +13,7 @@ mod rank_select;
 // pub use impls::columns::ColumnsRegion;
 // pub use impls::mirror::MirrorRegion;
 pub use impls::option::OptionRegion;
-// pub use impls::result::ResultRegion;
+pub use impls::result::ResultRegion;
 pub use impls::slice::SliceRegion;
 pub use impls::slice_owned::OwnedRegion;
 pub use impls::string::StringRegion;
@@ -492,13 +492,13 @@ mod tests {
 
     use super::*;
 
-    // #[test]
-    // fn test_readme() {
-    //     let r: Result<_, u16> = Ok("abc");
-    //     let mut c = FlatStack::default_impl::<Result<&str, u16>>();
-    //     c.copy(r);
-    //     assert_eq!(r, c.get(0));
-    // }
+    #[test]
+    fn test_readme() {
+        let r: Result<_, u16> = Ok("abc");
+        let mut c = <Result<&str, u16> as RegionPreference>::Region::default();
+        c.push(r);
+        assert_eq!(Ok("abc"), c.index(0));
+    }
 
     #[test]
     fn test_slice_string_onto() {
@@ -534,13 +534,13 @@ mod tests {
         assert!(slice.iter().eq(c.index(0)));
     }
 
-    // #[test]
-    // fn test_result() {
-    //     let r: Result<_, u16> = Ok("abc");
-    //     let mut c = <ResultRegion<StringRegion, MirrorRegion<_>>>::default();
-    //     let idx = copy(&mut c, r);
-    //     assert_eq!(r, c.index(idx));
-    // }
+    #[test]
+    fn test_result() {
+        let r: Result<_, u16> = Ok("abc");
+        let mut c = <ResultRegion<StringRegion, Vec<_>>>::default();
+        c.push(r);
+        assert_eq!(Ok("abc"), c.index(0));
+    }
 
     #[test]
     fn all_types() {
@@ -553,7 +553,8 @@ mod tests {
                 + Index
                 + Clone
                 + Clear
-        + HeapSize + Len,
+                + HeapSize
+                + Len,
             // Make sure that types are debug, even if we don't use this in the test.
             for<'a> R::ReadItem<'a>: Debug,
         {
@@ -658,18 +659,10 @@ mod tests {
         test_copy::<_, OptionRegion<StringRegion>>(Option::<&'static str>::None);
         test_copy::<_, OptionRegion<StringRegion>>(&Option::<&'static str>::None);
 
-        // test_copy::<_, ResultRegion<StringRegion, MirrorRegion<u8>>>(
-        //     Result::<&'static str, u8>::Ok("abc"),
-        // );
-        // test_copy::<_, ResultRegion<StringRegion, MirrorRegion<u8>>>(
-        //     &Result::<&'static str, u8>::Ok("abc"),
-        // );
-        // test_copy::<_, ResultRegion<StringRegion, MirrorRegion<u8>>>(
-        //     Result::<&'static str, u8>::Err(1),
-        // );
-        // test_copy::<_, ResultRegion<StringRegion, MirrorRegion<u8>>>(
-        //     Result::<&'static str, u8>::Err(2),
-        // );
+        test_copy::<_, ResultRegion<StringRegion, Vec<u8>>>(Result::<&'static str, u8>::Ok("abc"));
+        test_copy::<_, ResultRegion<StringRegion, Vec<u8>>>(&Result::<&'static str, u8>::Ok("abc"));
+        test_copy::<_, ResultRegion<StringRegion, Vec<u8>>>(Result::<&'static str, u8>::Err(1));
+        test_copy::<_, ResultRegion<StringRegion, Vec<u8>>>(Result::<&'static str, u8>::Err(2));
     }
 
     #[test]