Move the MergeFunction trait into its own module

src/lib.rs

@@ -196,17 +196,17 @@ mod block_writer;
 mod compression;
 mod count_write;
 mod error;
+mod merge_function;
 mod merger;
 mod metadata;
 mod reader;
 mod sorter;
 mod varint;
 mod writer;
 
-use either::Either;
-
 pub use self::compression::CompressionType;
 pub use self::error::Error;
+pub use self::merge_function::MergeFunction;
 pub use self::merger::{Merger, MergerBuilder, MergerIter};
 pub use self::metadata::FileVersion;
 pub use self::reader::{PrefixIter, RangeIter, Reader, ReaderCursor, RevPrefixIter, RevRangeIter};
@@ -219,50 +219,6 @@ pub use self::writer::{Writer, WriterBuilder};
 
 pub type Result<T, U = Infallible> = std::result::Result<T, Error<U>>;
 
-// TODO move this elsewhere
-pub trait MergeFunction {
-    type Error;
-    fn merge<'a>(
-        &self,
-        key: &[u8],
-        values: &[Cow<'a, [u8]>],
-    ) -> std::result::Result<Cow<'a, [u8]>, Self::Error>;
-}
-
-impl<MF> MergeFunction for &MF
-where
-    MF: MergeFunction,
-{
-    type Error = MF::Error;
-
-    fn merge<'a>(
-        &self,
-        key: &[u8],
-        values: &[Cow<'a, [u8]>],
-    ) -> std::result::Result<Cow<'a, [u8]>, Self::Error> {
-        (*self).merge(key, values)
-    }
-}
-
-impl<MFA, MFB> MergeFunction for Either<MFA, MFB>
-where
-    MFA: MergeFunction,
-    MFB: MergeFunction<Error = MFA::Error>,
-{
-    type Error = MFA::Error;
-
-    fn merge<'a>(
-        &self,
-        key: &[u8],
-        values: &[Cow<'a, [u8]>],
-    ) -> std::result::Result<Cow<'a, [u8]>, Self::Error> {
-        match self {
-            Either::Left(mfa) => mfa.merge(key, values),
-            Either::Right(mfb) => mfb.merge(key, values),
-        }
-    }
-}
-
 /// Sometimes we need to use an unsafe trick to make the compiler happy.
 /// You can read more about the issue [on the Rust's Github issues].
 ///

src/merge_function.rs

@@ -0,0 +1,46 @@
+use std::borrow::Cow;
+use std::result::Result;
+
+use either::Either;
+
+/// A trait defining the way we merge multiple
+/// values sharing the same key.
+pub trait MergeFunction {
+    type Error;
+    fn merge<'a>(&self, key: &[u8], values: &[Cow<'a, [u8]>])
+        -> Result<Cow<'a, [u8]>, Self::Error>;
+}
+
+impl<MF> MergeFunction for &MF
+where
+    MF: MergeFunction,
+{
+    type Error = MF::Error;
+
+    fn merge<'a>(
+        &self,
+        key: &[u8],
+        values: &[Cow<'a, [u8]>],
+    ) -> Result<Cow<'a, [u8]>, Self::Error> {
+        (*self).merge(key, values)
+    }
+}
+
+impl<MFA, MFB> MergeFunction for Either<MFA, MFB>
+where
+    MFA: MergeFunction,
+    MFB: MergeFunction<Error = MFA::Error>,
+{
+    type Error = MFA::Error;
+
+    fn merge<'a>(
+        &self,
+        key: &[u8],
+        values: &[Cow<'a, [u8]>],
+    ) -> Result<Cow<'a, [u8]>, Self::Error> {
+        match self {
+            Either::Left(mfa) => mfa.merge(key, values),
+            Either::Right(mfb) => mfb.merge(key, values),
+        }
+    }
+}