Bug #10795

to_s returns references to self if called on string

Added by fra.boffa (Francesco Boffa) over 5 years ago. Updated over 5 years ago.

Target version:
ruby -v:
ruby 2.1.5p273 (2014-11-13 revision 48405) [x86_64-darwin13.0]


This is not actually a bug, but rather a strong violation of the Principle of least astonishment.

Lately I found a bug in the Rails project I work to. There was a method concatenating two float values with a comma, converting them to string like this:

def coords_to_string
  latitude.to_s << "," << longitude.to_s

The bug happened when we passed latitude and longitude as strings instead of floats.

Actually, 5.12345.to_s returns a new string object and any operation made on that string wont affect the original 5.12345. Instead "5.12345".to_s will return the same instance of that string, so that the << method will affect the original string.

So we found that our latitude variable was growing on each call and after a while it become "5.12345,13.12345,13.12345,13.12345,13.12345,13.12345"

This was probably made like this for performance reasons, however we found it a clear violation of the POLA, whereas we expected to_s to always return a new instance of that string.

Hope, this may help.
Francesco Boffa

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