DEV Community

Discussion on: The types in TypeScript

peerreynders profile image
peerreynders • Edited on

I think your approach is heavily inspired by how folks solved stuff with classes.

Design by Contract is attributed to Bertrand Meyer in connection with the Eiffel OOPL (1986) but the "type first" notion appears elsewhere like in Clojure's "thinking in data, modeling in data, and working in data" which is most definitely not OO.

And the idea of "function types as contracts" is up-to-date - 3.7.1 Types and Contracts.

Explicit types serve as deliberate "check points" during type checking/linting.

Is faster because we focus on the implementation, and the types are derived from that.

Expedience is always fielded as the primary motivation for "implementation first, contract last" approaches. But more often than not, contract last approaches save you time in the short term but create problems (that could be avoided by actively managing your types) in the long term (TTIS - Time-To-Initial-Success).

To some degree it's like saying "I know that JSDoc annotations are helpful for maintenance but keeping them in sync with the code slows me down so it's not worth it". Types are part of the application's specification that are supposed make it easier to reason about the code, so it helps if they are not buried somewhere in the implementation.

I guess the lesson here is: just because TypeScript is being used doesn't actually reveal whether the potential of types is being leveraged to maximum effect (to the extend that is even possible in TypeScript).

Aside: