The operation "empty_string += string" is now significantly faster. This is rather common in code that works with buffers. Previously it was, somewhat surpisingly, significantly faster to write code like: if( strlen( x ) ) x += str; else x = str; than it was to simply add the str to x regardless of whether or not x already had contents. Now the check is done in `+() instead. However, it still does not handle things like "" + str + "", which might perhaps be useful, but is significantly less common in real code. str + "" was already handled.