Add .entries(), .keys(), .values() record traversals #81

akheron · 2021-04-12T19:19:39Z

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cowboyd · 2021-04-14T13:33:46Z

Cool! I have some questions with this API, what would be the best way to do the following?

a. add an entry?
b. remove an entry?
c. remove a key and have it remove the entry?
d. remove a value and have it remove the entry?

akheron · 2021-04-14T13:49:01Z

Unfortunately, traversals don’t allow that kind of stuff in general. Introducing something like RemovableTraversal could make sense, though, especially if it would allow returning a special “remove me” value from modify to remove the element at focus.

akheron · 2021-04-14T13:50:11Z

Also, typescript seems to have really hard time to type check certain things with this pr’s modifications, so I’m not sure if this can be merged at all.

akheron · 2021-04-14T13:52:48Z

One more thing: If you’re using optics from a JavaScript project (instead of TypeScript), I highly recommend https://github.com/calmm-js/partial.lenses. It’s much more feature complete than optics-ts and supports stuff you mentioned. It’s much harder to implement those in optics-ts because the restrictions imposed by the type system need to be taken into account.

cowboyd · 2021-04-15T07:00:33Z

That's good to know. I was able to use optics-ts to remove and add from traversals on runkit which is, of course, untyped. So it is at least possible, but I don't know if what I was doing was a hack, and how it might work with the type system. I don't know if you had a chance to read it here https://runkit.com/cowboyd/optics-ts-record-traversal

I will have a look at partial.lenses

cowboyd · 2021-07-02T17:38:47Z

@akheron

Also, typescript seems to have really hard time to type check certain things with this pr’s modifications, so I’m not sure if this can be merged at all.

What is missing from TypeScript to be able to do this? We're definitely not using JavaScript, so this library seems like our best hope.

Unfortunately, traversals don’t allow that kind of stuff in general. Introducing something like RemovableTraversal could make sense, though, especially if it would allow returning a special “remove me” value from modify to remove the element at focus.

What would that API look like?