Why do some of the functions use StringBuilder (no internal synchronization) and some use StringBuffer (provides internal synchronization). Using the latter is probably a mistake.
The first function -- reverse -- uses StringBuilder#reverse() to reverse the character sequence in place, and then calls StringBuilder#toString() to yield a String. Why is the final step necessary? Since StringBuilder implements CharSequence, isn't it sufficient to just return the StringBuilder? That's what the function signature promises. Calling toString() makes yet another copy of the data, so it's best avoided. Some of these functions construct instances of class StringBuilder using its default constructor, which gives it a default capacity. But most of the functions also know at the outset some reasonable size for the buffer. For instance, function `replace-first-by' could reasonably use the length of its argument "s" as the size of the buffer, even though the replacement for some matched substring may increase the overall length. Why does function `replace-first' unconditional call CharSequence#toString() on its argument "s", when in several cases just using "s" as a CharSequence would be fine. Again, calling CharSequence#toString() might make a copy of the data, depending on whether the CharSequence was actually a String or something like a StringBuilder. The implementation of a function like `trim' could be more efficient, given that it's allowed to return a CharSequence. You can construct a StringBuilder of length equal to the source CharSequence, then walk the source sequence from the beginning, skipping over all whitespace, copying the non-whitespace characters, repeating until you hit the end of the source string. The "right trim" behavior is a little tricky, as you have to suspend the copying upon encountering whitespace, but but back up and copy that whitespace upon encountering something else before the end of the source string. Alternately, just walk backward from the end of the source string. The bonus is that you only copy the data once. With the current implementation, calling CharSequence#toString() might copy the data once, and calling String#trim() will copy it again. Rounding out the review, function `trim-newline' doesn't have to call toString() on the CharSequence yielded by CharSequence#subSequence(), as it already promises to return a CharSequence. Most Java code poisons its string manipulation efficiency by always promising to return String rather than CharSequence. You've done better in your signatures here, so I'm just encouraging you to avoid String and the extra copies it forces. -- Steven E. Harris -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
