README.md

RBS Steep Demo

Demo (lack of) type narrowing.

Usage

1. Clone this repo.

2. Install dependencies: bundle install

3. Check types with Steep: bundle exec steep check rbs_steep_demo.rb

4. Note the following error is reported:

   rbs_steep_demo.rb:12:18: [error] Type `(::Integer | nil)` does not have method `+`
   │ Diagnostic ID: Ruby::NoMethod
   │
   └     @maybe_number + 1
                       ~
   
   Detected 1 problem from 1 file
   

5. Consider that the early return on rbs_steep_demo.rb#L10 (return if @maybe_number.nil?) should narrow the type of @maybe_number to Integer, and that Integer has a method +.

References

• RBS
• Steep