Use transient to accumulate row contents in csv parser

Another small perf advantage on hmrc-rts-small-area.csv ~1% faster

src/csv2rdf/tabular/csv/reader.clj

@@ -286,30 +286,30 @@
  to the dialect trim mode."
  [^String row-content source-row-number {:keys [^Character escapeChar ^Character quoteChar ^Character delimiter trim-mode] :as options}]
  (if (zero? (.length row-content))
-  []
-  (let [;;NOTE: cells are parsed slightly differently depending on
-  ;;whether the quote and escape characters are the same or
-  ;;different. Each parser parses the next cell contents
-  ;;from the specified starting position within the string
-  ;;and returns a map containing the parsed cell contents
-  ;;and the index within the string to continue
-  ;;parsing. This should always point to the delimiter
-  ;;character or be one passed the end of the string.
-  cell-parser (if (= escapeChar quoteChar)
-  parse-cell-double-quote
-  parse-cell-escape)] 
-   (loop [idx 0
- cells []]
- (let [{:keys [cell ^long next-index]} (cell-parser row-content source-row-number idx options)]
- ;;if there is any remaining input, next-index should refer to the delimiter
- ;;consume it and move to the start of the next cell
- ;;otherwise entire row has been parsed
- ;;TODO: move quoted cell followed by delimiter validation stuff here?
- (if (< next-index (.length row-content))
- (let [next-char (.charAt row-content next-index)]
- #_(assert (= delimiter next-char "Expected delimiter after parsed cell"))
- (recur (inc next-index) (conj cells (trim-cell cell trim-mode))))
- (conj cells (trim-cell cell trim-mode))))))))
+ []
+ (let [ ;;NOTE: cells are parsed slightly differently depending on
+ ;;whether the quote and escape characters are the same or
+ ;;different. Each parser parses the next cell contents
+ ;;from the specified starting position within the string
+ ;;and returns a map containing the parsed cell contents
+ ;;and the index within the string to continue
+ ;;parsing. This should always point to the delimiter
+ ;;character or be one passed the end of the string.
+ cell-parser (if (= escapeChar quoteChar)
+ parse-cell-double-quote
+ parse-cell-escape)]
+ (persistent! (loop [idx 0
+  cells (transient [])]
+  (let [{:keys [cell ^long next-index]} (cell-parser row-content source-row-number idx options)]
+  ;;if there is any remaining input, next-index should refer to the delimiter
+  ;;consume it and move to the start of the next cell
+  ;;otherwise entire row has been parsed
+  ;;TODO: move quoted cell followed by delimiter validation stuff here?
+  (if (< next-index (.length row-content))
+  (let [next-char (.charAt row-content next-index)]
+  #_(assert (= delimiter next-char "Expected delimiter after parsed cell"))
+  (recur (inc next-index) (conj! cells (trim-cell cell trim-mode))))
+  (conj! cells (trim-cell cell trim-mode)))))))))
 
 (s/def ::source-row-number (s/and integer? pos?))
 (s/def ::cells (s/coll-of string? :kind vector? :into []))