Make ReadItem: CopyOnto<Self>

Cargo.toml

@@ -23,7 +23,3 @@ default = ["serde"]
 debug = 2
 codegen-units = 1
 lto = true
-
-[[bench]]
-name = "bench"
-harness = false

src/impls/mirror.rs

@@ -16,7 +16,7 @@ impl<T> Default for MirrorRegion<T> {
     }
 }
 
-impl<T: Index> Region for MirrorRegion<T> {
+impl<T: Index + CopyOnto<Self>> Region for MirrorRegion<T> {
     type ReadItem<'a> = T where T: 'a;
     type Index = T;
 

src/impls/slice.rs

@@ -9,19 +9,18 @@ use crate::{CopyOnto, Region, ReserveItems};
 #[derive(Debug, Clone)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub struct SliceRegion<C: Region> {
-    // offsets: Vec<usize>,
     slices: Vec<C::Index>,
     inner: C,
 }
 
 impl<C: Region> Region for SliceRegion<C> {
-    type ReadItem<'a> = (&'a C, &'a [C::Index]) where Self: 'a;
+    type ReadItem<'a> = ReadSlice<'a, C> where Self: 'a;
     type Index = (usize, usize);
 
     #[inline]
     fn index(&self, (start, end): Self::Index) -> Self::ReadItem<'_> {
         let slice = &self.slices[start..end];
-        (&self.inner, slice)
+        ReadSlice(&self.inner, slice)
     }
 
     #[inline]
@@ -37,7 +36,6 @@ impl<C: Region> Region for SliceRegion<C> {
 
     #[inline]
     fn clear(&mut self) {
-        // self.offsets.clear();
         self.slices.clear();
         self.inner.clear();
     }
@@ -52,6 +50,58 @@ impl<C: Region> Default for SliceRegion<C> {
     }
 }
 
+/// A helper to read data out of a slice region.
+#[derive(Debug)]
+pub struct ReadSlice<'a, C: Region>(pub &'a C, pub &'a [C::Index]);
+
+impl<'a, C: Region> ReadSlice<'a, C> {
+    /// Read the n-th item from the underlying region.
+    #[inline]
+    pub fn get(&self, index: usize) -> C::ReadItem<'_> {
+        self.0.index(self.1[index])
+    }
+
+    /// The number in this slice.
+    pub fn len(&self) -> usize {
+        self.1.len()
+    }
+
+    /// Test if this slice is empty.
+    pub fn is_empty(&self) -> bool {
+        self.1.is_empty()
+    }
+}
+
+impl<'a, C: Region> Clone for ReadSlice<'a, C> {
+    #[inline]
+    fn clone(&self) -> Self {
+        Self(self.0, self.1)
+    }
+}
+
+impl<'a, C: Region> Copy for ReadSlice<'a, C> {}
+
+impl<'a, C: Region> IntoIterator for ReadSlice<'a, C> {
+    type Item = C::ReadItem<'a>;
+    type IntoIter = ReadSliceIter<'a, C>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        ReadSliceIter(self.0, self.1.iter())
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct ReadSliceIter<'a, C: Region>(&'a C, std::slice::Iter<'a, C::Index>);
+
+impl<'a, C: Region> Iterator for ReadSliceIter<'a, C> {
+    type Item = C::ReadItem<'a>;
+
+    #[inline]
+    fn next(&mut self) -> Option<Self::Item> {
+        self.1.next().map(|idx| self.0.index(*idx))
+    }
+}
+
 impl<'a, C, T: 'a> CopyOnto<SliceRegion<C>> for &'a [T]
 where
     C: Region,
@@ -136,13 +186,13 @@ where
     }
 }
 
-impl<'a, C: Region + 'a> CopyOnto<SliceRegion<C>> for &'a (&'a C, &'a [C::Index])
+impl<'a, C: Region + 'a> CopyOnto<SliceRegion<C>> for ReadSlice<'a, C>
 where
     C::ReadItem<'a>: CopyOnto<C>,
 {
     #[inline]
     fn copy_onto(self, target: &mut SliceRegion<C>) -> <SliceRegion<C> as Region>::Index {
-        let (container, indexes) = self;
+        let ReadSlice(container, indexes) = self;
         let start = target.slices.len();
         target.slices.extend(
             indexes
@@ -158,10 +208,10 @@ where
     {
         target
             .slices
-            .reserve(items.clone().map(|(_c, is)| is.len()).sum());
+            .reserve(items.clone().map(|ReadSlice(_c, is)| is.len()).sum());
         CopyOnto::reserve_items(
             &mut target.inner,
-            items.flat_map(|(c, is)| is.iter().map(|i| c.index(*i))),
+            items.flat_map(|ReadSlice(c, is)| is.iter().map(|i| c.index(*i))),
         )
     }
 }

src/impls/string.rs

@@ -2,7 +2,7 @@
 use serde::{Deserialize, Serialize};
 
 use crate::impls::slice_copy::CopyRegion;
-use crate::{Containerized, CopyOnto, Region, ReserveItems, SliceRegion};
+use crate::{Containerized, CopyOnto, Region, ReserveItems};
 
 /// A region to store strings and read `&str`.
 #[derive(Default, Debug, Clone)]
@@ -13,7 +13,7 @@ pub struct StringRegion {
 
 impl Region for StringRegion {
     type ReadItem<'a> = &'a str where Self: 'a ;
-    type Index = <SliceRegion<CopyRegion<u8>> as Region>::Index;
+    type Index = <CopyRegion<u8> as Region>::Index;
 
     #[inline]
     fn index(&self, index: Self::Index) -> Self::ReadItem<'_> {

src/lib.rs

@@ -22,7 +22,7 @@ impl<T: Copy> Index for T {}
 /// A region to store data.
 pub trait Region: Default {
     /// The type of the data that one gets out of the container.
-    type ReadItem<'a>
+    type ReadItem<'a>: CopyOnto<Self>
     where
         Self: 'a;
 
@@ -336,12 +336,15 @@ mod tests {
 
     #[test]
     fn all_types() {
-        fn test_copy<T, C: Region>(t: T)
+        fn test_copy<T, C: Region + Clone>(t: T)
         where
             T: CopyOnto<C>,
         {
             let mut c = FlatStack::default();
             c.copy(t);
+
+            let mut cc = c.clone();
+            cc.copy(c.get(0));
         }
 
         test_copy::<_, StringRegion>(&"a".to_string());
@@ -413,4 +416,17 @@ mod tests {
 
         test_copy::<_, <(u8, u8) as Containerized>::Region>((1, 2));
     }
+
+    #[test]
+    fn slice_region_read_item() {
+        let mut c = FlatStack::<SliceRegion<MirrorRegion<u8>>>::default();
+        c.copy(vec![1, 2, 3]);
+
+        let mut r = SliceRegion::<MirrorRegion<u8>>::default();
+        let idx = [1, 2, 3].copy_onto(&mut r);
+        let read_item = r.index(idx);
+        let _read_item2 = read_item.clone();
+        let _read_item3 = read_item;
+        assert_eq!(vec![1, 2, 3], read_item.into_iter().collect::<Vec<_>>());
+    }
 }