Phantom types

[Neurrone]

Outline:

• What are phantom types, and how they can be used?
• Why use phantom types?

Slides

[Neurrone]

PUMA outline:

1. Audience: fellow CS3281/2 students
2. Objective: To encourage use of phantom types
3. Topic: Prevent bugs at compile-time with phantom types
4. PUNCH: Show real scenario that could have been prevented using phantom types
5. WIIFY: Learn a technique that you can immediately use to write code with less bugs.
6. Promise:
   • WHAT are phantom types?
   • Why are phantom types worth using?
   • When to/not to use phantom types?
7. Content:
   • WHAT are phantom types?
     • Explained through an example
     • Key point: phantom types is a technique that cleverly uses type parameters to augment types with extra info
   • WHY use phantom types?
     • Encode invariants into the type system so we can use the compiler to find bugs
     • Easy
     • No runtime costs
     • Support: demonstrate with examples
     • Key point: Using phantom types is worth doing because it lets you catch some bugs at compile-time
   • When to/not to use?
8. Key points / summary statement / elevator pitch
   • Phantom types is a technique where unused type parameters in types can be used to augment the type with extra info.
   • Distinguish types that are otherwise identical at compile-time, e.g if the type has multiple states - sanitized vs unsanitized, units of measurement
   • Use only when pros > cons (like design patterns)
   • Easy and worth doing,
9. Call to action: Let’s start using phantom types!

Do: start using phantom types
Believe: using phantom types is easy and worthwhile
Know: what are phantom types, why and when they are useful