The Lens Pattern in TypeScript

functional.christmas

11 pointskvalle4 comments

Genuinely asking as I've had to tackle modification of large deeply nested immutable objects in JS. Because of the large and varied object, I used a generic approach of set/get functions that could take paths using https://github.com/mariocasciaro/object-path-immutable

Use of this lens pattern as given in the article seems to lead to a lot more boilerplate with lenses that have knowledge of object structure, which doesn't seem optimal. So I must be missing what this specific+compositional approach gives over using something like object-path-immutable. Perhaps they are two approaches for two different situations?

Lenses are type-safe, so if you care about type-safety then object/json paths are not really a feasible option. Regarding the boilerplate in this post, that is mainly a side-effect of demonstrating how lenses work. If you use a library like monocle-ts the boilerplate is reduced drastically (see: https://github.com/gcanti/monocle-ts).

Aaah I see, I had completely glossed over the type-safety aspect which makes the difference. Thanks, and thanks for the reference to monocle-ts.

Interesting approach!

Reply on news.ycombinator.com