Nil

nil is a magic object

There Is No Spoon

nil is the object that means "there is no object"

Experiment

fruit = "apple"
fruit = nil
fruit.reverse

Read the error!

Errors are good

They tell you

• you made a mistake
• what that mistake was
• (sometimes) how to fix it

Interpret this error:

fruit.reverse
NoMethodError: undefined method `reverse' for nil:NilClass

Fail Fast, Fail Often

• Ruby has a "fail fast" philosophy
• Is this a good idea?
• Why or why not?