Discussion on: Convince me that types are awesome

[jmc]

I wouldn't try to convince anyone to use types. Or to avoid them, either. They're useful. But silver bullets are expensive. As I see it:

Pros:

• annotating types is often cheap
• you can't forget to check (i.e. what type systems guarantee, they guarantee fully)
• better IDE hints
• they serve as a rough documentation for libraries
• worry-free refactoring

Cons:

• typecheckers check precisely the things that are easy for an algorithm to check, i.e. nothing to do with your problem domain
  • you can fix some of that by representing your domain as types, but then your algorithms aren't reusable
    • you can fix some of that by adding abstractions to the type system, but that raises the cost of annotating
• you probably still have null references
  • you can fix that (to a degree) with option/maybe/whatever... which raises the cost of writing code
• "static" bugs like typos and passing in arguments of the wrong type are easy to fix