split: minor parallel_split optimizations; wordsmith output summary

parallel_split()
- remove unnecessary var args, cloning self
- amortized `write_row` byterecord allocation for hot write loop

output summary now accounts for singular chunk

Author: jqnatividad

src/cmd/split.rs

@@ -147,7 +147,7 @@ impl Args {
 
         if !self.flag_quiet {
             eprintln!(
-                "Wrote {} chunks to '{}'. Rows/chunk: {} Num records: {}",
+                "Wrote {} chunk/s to '{}'. Rows/chunk: {} Num records: {}",
                 nchunks + 1,
                 Path::new(&self.arg_outdir).canonicalize()?.display(),
                 chunk_size,
@@ -159,16 +159,15 @@ impl Args {
     }
 
     fn parallel_split(&self, idx: &Indexed<fs::File, fs::File>) -> CliResult<()> {
-        let args = self.clone();
         let chunk_size;
         let idx_count = idx.count();
 
         #[allow(clippy::cast_precision_loss)]
-        let nchunks = if let Some(flag_chunks) = args.flag_chunks {
+        let nchunks = if let Some(flag_chunks) = self.flag_chunks {
             chunk_size = (idx_count as f64 / flag_chunks as f64).ceil() as usize;
             flag_chunks
         } else {
-            chunk_size = args.flag_size;
+            chunk_size = self.flag_size;
             util::num_of_chunks(idx_count as usize, self.flag_size)
         };
         if nchunks == 1 {
@@ -177,38 +176,39 @@ impl Args {
             return self.sequential_split();
         }
 
-        util::njobs(args.flag_jobs);
+        util::njobs(self.flag_jobs);
 
         // safety: we cannot use ? here because we're in a closure
         (0..nchunks).into_par_iter().for_each(|i| {
-            let conf = args.rconfig();
+            let conf = self.rconfig();
             // safety: safe to unwrap because we know the file is indexed
             let mut idx = conf.indexed().unwrap().unwrap();
             // safety: the only way this can fail is if the file first row of the chunk
             // is not a valid CSV record, which is impossible because we're reading
             // from a file with a valid index
             let headers = idx.byte_headers().unwrap();
 
-            let mut wtr = args
+            let mut wtr = self
                 // safety: the only way this can fail is if we cannot create a file
-                .new_writer(headers, i * chunk_size, args.flag_pad)
+                .new_writer(headers, i * chunk_size, self.flag_pad)
                 .unwrap();
 
             // safety: we know that there is more than one chunk, so we can safely
             // seek to the start of the chunk
             idx.seek((i * chunk_size) as u64).unwrap();
+            let mut write_row;
             for row in idx.byte_records().take(chunk_size) {
-                let row = row.unwrap();
-                wtr.write_byte_record(&row).unwrap();
+                write_row = row.unwrap();
+                wtr.write_byte_record(&write_row).unwrap();
             }
             // safety: safe to unwrap because we know the writer is a file
             // the only way this can fail is if we cannot write to the file
             wtr.flush().unwrap();
         });
 
-        if !args.flag_quiet {
+        if !self.flag_quiet {
             eprintln!(
-                "Wrote {} chunks to '{}'. Rows/chunk: {} Num records: {}",
+                "Wrote {} chunk/s to '{}'. Rows/chunk: {} Num records: {}",
                 nchunks,
                 Path::new(&self.arg_outdir).canonicalize()?.display(),
                 chunk_size,