Nil

nil is a magic object

There Is No Spoon

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

Q: What is the sound of one hand clapping?

A: nil

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

null pointer errors

• null pointer errors are very common
• the trick is reading the error and figuring out
  1. where it happened (*which line*)
  2. which variable was null
• often once you know which, knowing why is obvious
• or at least tracing back the logic is possible

If You're Going To Fail...

Two philosophies:

• fail hard, fail fast
• keep calm and carry on

Which idea is better?

Why or why not?

Fail Fast, Fail Often

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