In real code, we found a very, very slow loop. Changing two characters:
+=is about 100 seconds.<<is around 1/3 of a second.
Using += on a string creates a copy and then discards the original, while << allows the ruby interpreter to intelligently resize the buffer.
The only gotcha is that << will mutate your string object, which means that it’s not safe to use on a method’s parameters. #dup those strings, if you need to append to them.
