Let’s say you read settings from a YAML file and have some sort of settings object. Then you check if certain options are set with custom values or you have to set default/fall-back values on them. If you are dealing with Boolean options you have to be careful … as I had to find out myself.
Initially you would probably do something like the following to set a default value on a Boolean option:
settings[:some_option]||=true# set default value if nothing set
Do you see the problem? What happens if the option was deliberately set to
false ? You would overwrite it because both cases nil (i.e. nothing set) and false would evaluate to false in the context of the ||= operator and you would in both cases assign the right hand value (and overriding an explicit user choice in one case) … *ouch*.
So the correct solution is something like the following: