Transforming object to class instance while preserving the types

[icy totem]

Hi! I've got a code where I have defined class Opt<T> {...} and class Group<...> { ... }. Group contains other Groups and Opts. I also have a plain object that does not use these classes and I want to convert it to instances of these classes while preserving types.

I know that code is worth more than 1000 words, so here is the example - I want to write a function which transforms input to output. The body of the function does not matter, I have trouble with expressing the type signature. Is it somehow possible?

https://www.typescriptlang.org/play?ssl=23&ssc=1&pln=23&pc=12#code/MYGwhgzhAEDyAOAXAPAFQHzQN4Chr+gBMBTAMzAFcREAuaVPAkiYAJwEsl2B7AOzoiIOvAOaN8wPoNYVgibqwAUwUiLq4CmomUrU6DLU2IsOXPgKHtR46AF8AlNhubEAC3YQAdCXJVE0AF5oFRFvHT9nAjcPMJNORB5eQODVWLZ4xJtbHGycRABPeGI4M14ANTAQCmKg6SsRaAAfaAAjbm4QYjAk5t4KAFsW4lYm6DrRAG0AXTzC4oBBXnyEBL5kleQVxIqq4nRZopLV3ggAJWJJVkJk88vCZHGRABpoReXS-YLDgHFWbgp4GcLgprkFbiCHpZRC83r9-vB9jgrIhhuRgAslnCAU5NNxShA6FspOCrjYRH8AQToFjASTCDkcDhQJAYDTNvjoMQAB4o3iEGBEk50l40mDc3n86kU2nAq6YDQEPHHKmCmBBLC2aCQI6JCBk6VU0XJDVa1kGmySE5CWTyJQhAD86mgSt1jp1UgA3NByfCIG6jQ4cYZglJ-C6pMkHZ5wydIvh2KRoIoYzAAIRBPogECOBXBqLuLwp5IpuN2UuWwTeg2R1T2zw+ymlhNJhuA6Dp6CZ7NBvP4aJeVtqqu+0vZTTZXJM0PQKzwCj+dX633qUsiACMK97ivxm63WhjG57e8MPl0tGgAFYnqXj8x0qU6AByA-aOKlR834O2a-H3GlABMu6-lop5+HQABsP7ASBxj3scT4xv+r5wYkH7QWWx7fp++CDkBv7rgA+uueHoSmJHoduxwAMzkRRMG+Ho0AAOxQXReZ3qY8HQM+pRUchnGodhv5jmxInAWJvYSeOWQMlOVrOvOc4Lp2xAAO5SvCii5sOlK0d6h68GpGkAlpQlkUex4HnQhnqSsplsdoDHnleQnsbBAnmNxL4cRkfBodBDisb+iHWUZdnaehoGMZBrnBj5D5eQB-G+bw-nifYQlYceuEWXuhHESp6k0vZbHmRFpW8aFtlICVDknuEjEsbFwHxVxPHUcl77NZJGUOVJe4OJlo69QQE72EAA

[slim thunder]

@icy totem Here's a shortened URL of your playground link! You can remove the full link from your message.

wdanilo#2781

Playground Link

Preview:ts ... class Group< Options extends OptionsRecord ...

[icy totem]

Also, to explain why I need it. I want to store the config in json file and load it to both JS and Rust code.

[polar spade]

i don't believe this is possible

https://github.com/microsoft/TypeScript/issues/32063

[icy totem]

@polar spade oh actually I am able to import json and get it properly typed in TS

[polar spade]

oh?!!!

!:narrow

[slim thunder]

T6#2591

`!t6:narrow`: Playground Link

Preview:ts type _Narrow<T, U> = [U] extends [T] ? U : Extract<T, U> type Narrow<T = unknown> = | _Narrow<T, 0 | number & {}> | _Narrow<T, 0n | bigint & {}> | _Narrow<T, "" | string & {}> | _Narrow<T, boolean> | _Narrow<T, symbol> | _Narrow<T, []> | _Narrow<T, { [_: PropertyKey]: Narrow }> | (T extends object ? { [K in keyof T]: Narrow<T[K]> } : never) | Extract<{} | null | undefined, T> ...

[icy totem]

import * as myjson from './file.json' works

[polar spade]

?!!!

oh

you don't need the actual names at the type level

just a heads up though

[icy totem]

no, it just works. And all the nested fields are typed correctly

[polar spade]

but is default typed as 5

[icy totem]

no, as number

and thats enough for me

[polar spade]

right, that's what i was implying here

[icy totem]

oh, gotcha. Anyway, this is enough of type info for me. Do you think it is possible. to transform the types as I want then ?

[polar spade]

i'm guessing you want to be able to access methods on Opt and Group?

[icy totem]

thats right

[polar spade]

uhh

note that you don't have the javascript code to turn the options and groups into objects

so you'd have to implement that later

[icy totem]

sure, but thats simple

[slim thunder]

n_n#2622

Playground Link

Preview:```ts
...
class Group<
Options extends
| OptionsRecord
| undefined = undefined,
Groups extends GroupsRecord | undefined = undefined

{
options = {} as {
[K in keyof Options]: Opt<
NonNullable<Options>[K]["default"]

}
groups = {} as {
[K in keyof Groups]: Group<
NonNullable<Groups>[K]["options"],
NonNullable<
...```

[polar spade]

yup

so

something liek this should work

if that's maintainable enough

[icy totem]

Hmm, it doesnt 😦

Here, option1 is not typed as Opt<...> .

Anyway, this does not have to be done via constructor, it can be just a function convert that converts between these two things

I mean, a function convert(input) that would return output

[polar spade]

it does

check the code at the bottom

[icy totem]

ohhh, interesting, hmmm, I dont understand why, brb, trying to parse / understand it

[polar spade]

it does a transformation on the type parameters

[icy totem]

this is so tricky!

[polar spade]

(see the types of options and groups)

[polar spade]

yeah! not sure if there's a nicer way to do it... but i wouldn't be too sure, because you do have to change the type to the class at some point

also note that typescript may not be smart enough to infer the types of this.options = correctly even after you have a correct implementation

and so you may need to leave the unsafe type assertions there

[icy totem]

This has onl yone problem. ... output2 type still does not mention Opt, it mentions only plain object strcutre. I understand it works, because we are making type transformation in the field, but I also have afuntion merge which merges 2 groups together, like:

merge<Other extends AnyGroup>(other?: Other | null): this & Other {...}

^^^ This is a method in group. Which woild not work if Id try to merge a group created from a plain object and a hand-written one, right ?

[polar spade]

nah it would

well actually

hmm

well remember (or note that?) in typescript, it's only the shape that matters

TS doesn't care about generic parameters, it cares about whether options is the right type

add to that the fact that AnyGroup actually accepts even the plain object...

[icy totem]

damn, it works

ok, its a type system that I am completely not used to

thank you so so so so much @polar spade ❤️

Ehh, how I could pay you back for all your help? 😦

[polar spade]

i uhhh

honestly, going through the effort of making a playground and making it easy to help is more than enough tbh

anyway...

!close