Make CodecRegion generic over codecs

Signed-off-by: Moritz Hoffmann <[email protected]>

src/codec.rs

@@ -70,14 +70,15 @@ pub fn consolidate_slice<T: Ord>(slice: &mut [(T, usize)]) -> usize {
     offset
 }
 
+/// A region that encodes its data in a codec `C`.
 #[derive(Default, Debug)]
-struct CodecRegion {
+pub struct CodecRegion<C: Codec> {
     inner: CopyRegion<u8>,
-    codec: DictionaryCodec,
+    codec: C,
     staging: Vec<u8>,
 }
 
-impl Region for CodecRegion {
+impl<C: Codec> Region for CodecRegion<C> {
     type ReadItem<'a> = &'a [u8]
     where
         Self: 'a;
@@ -92,8 +93,8 @@ impl Region for CodecRegion {
         let codecs = regions.clone().map(|r| &r.codec).collect::<Vec<_>>();
         let codecs: Result<[_; 2], _> = codecs.try_into();
         let codec = match codecs {
-            Ok(codecs) => DictionaryCodec::new_from(codecs),
-            Err(_) => DictionaryCodec::default(),
+            Ok(codecs) => C::new_from(codecs),
+            Err(_) => C::default(),
         };
         Self {
             inner: CopyRegion::merge_regions(regions.map(|r| &r.inner)),
@@ -120,20 +121,14 @@ impl Region for CodecRegion {
     }
 }
 
-impl CopyOnto<CodecRegion> for &[u8] {
-    fn copy_onto(self, target: &mut CodecRegion) -> <CodecRegion as Region>::Index {
+impl<C: Codec> CopyOnto<CodecRegion<C>> for &[u8] {
+    fn copy_onto(self, target: &mut CodecRegion<C>) -> <CodecRegion<C> as Region>::Index {
         target.staging.clear();
         target.codec.encode(self, &mut target.staging);
         target.staging.as_slice().copy_onto(&mut target.inner)
     }
 }
 
-impl<'a> CopyOnto<CodecRegion> for std::iter::Once<&'a [u8]> {
-    fn copy_onto(mut self, target: &mut CodecRegion) -> <CodecRegion as Region>::Index {
-        self.next().unwrap_or(&[]).copy_onto(target)
-    }
-}
-
 /// TODO
 pub trait Codec: Default + 'static {
     /// Decodes an input byte slice into a sequence of byte slices.
@@ -370,12 +365,12 @@ mod misra_gries {
 
 #[cfg(test)]
 mod tests {
-    use super::{Codec, CodecRegion};
+    use super::{Codec, CodecRegion, DictionaryCodec};
     use crate::*;
 
     #[test]
     fn test_simple() {
-        let mut r = CodecRegion::default();
+        let mut r = CodecRegion::<DictionaryCodec>::default();
 
         for _ in 0..1000 {
             let index = "abc".as_bytes().copy_onto(&mut r);