style: Warn on unnecessary use of iter and fix all cases

This is more idiomatic than calling `iter` explicitly.

src/encoders/integer.rs

@@ -57,7 +57,7 @@ pub fn encode_all<'a>(src: &mut Vec<i64>, dst: &'a mut Vec<u8>) -> Result<(), Bo
             dst.reserve_exact(cap - dst.capacity());
         }
         dst.push((Encoding::Uncompressed as u8) << 4);
-        for delta in deltas.iter() {
+        for delta in &deltas {
             dst.extend_from_slice(&delta.to_be_bytes());
         }
         return Ok(());
@@ -201,7 +201,7 @@ fn decode_simple8b(src: &[u8], dst: &mut Vec<i64>) -> Result<(), Box<dyn Error>>
     simple8b::decode_all(&src[8..], &mut res);
     // TODO(edd): fix this. It's copying, which is slowwwwwwwww.
     let mut next = dst[0];
-    for v in res.iter() {
+    for v in &res {
         next += zig_zag_decode(*v);
         dst.push(next);
     }

src/encoders/timestamp.rs

@@ -57,7 +57,7 @@ pub fn encode_all<'a>(src: &mut Vec<i64>, dst: &'a mut Vec<u8>) -> Result<(), Bo
         }
 
         dst.push((Encoding::Uncompressed as u8) << 4);
-        for delta in deltas.iter() {
+        for delta in &deltas {
             dst.extend_from_slice(&delta.to_be_bytes());
         }
         return Ok(());
@@ -238,7 +238,7 @@ fn decode_simple8b(src: &[u8], dst: &mut Vec<i64>) -> Result<(), Box<dyn Error>>
     let mut next = dst[dst.len() - 1];
     if scaler > 1 {
         // TODO(edd): fix this. It's copying, which is slowwwwwwwww.
-        for v in res.iter() {
+        for v in &res {
             next += (v * scaler) as i64;
             dst.push(next);
         }
@@ -246,7 +246,7 @@ fn decode_simple8b(src: &[u8], dst: &mut Vec<i64>) -> Result<(), Box<dyn Error>>
     }
 
     // TODO(edd): fix this. It's copying, which is slowwwwwwwww.
-    for v in res.iter() {
+    for v in &res {
         next += *v as i64;
         dst.push(next);
     }

src/lib.rs

@@ -1,4 +1,5 @@
 #![deny(rust_2018_idioms)]
+#![warn(clippy::explicit_iter_loop)]
 
 use std::{error, fmt};
 

src/storage/rocksdb.rs

@@ -638,7 +638,7 @@ impl RocksDB {
         }
 
         // do the index writes from the in temporary in memory map
-        for (k, v) in index_map.iter() {
+        for (k, v) in &index_map {
             let _ = batch.put_cf(index_cf, k, v.serialize().unwrap());
         }