Infer the types from an object

[last dragon]

Hi, I have this use case where I want to turn a "simple" object into a more complex one, and also for the types.
I am not sure how to make the types work with this.

in the end I want to have a type, preferably as "const" that I can access

This is what I have so far:
https://www.typescriptlang.org/play?#code/JYOwLgpgTgZghgYwgAgMrALYAcA2KDeAUMsgNoDWEAngFzIDOYUoA5gLp2PMgvIA+aTLgik2AbkIBfQoVCRYiFAElIGVE1bIiJAG5wcAVwicNPCSRBwMxhqZZSZc6PCTIVEDAEEoUOFS3EyHqGNu5qdqLmyJbWJtz20rLgzorIAMIA9th4AB4BJBTUcawcbqrq8fzpWcI5kQ6ECBkgjMigMNDIALzIABQAJnBgcHTo2RAAlHSZ43ldAHz5yE0tYMhQEPQGOGDTNbndWpJRMBlQfSutlP6gyIPDE0skl2vBRof3cIVU4oEkwDA+mAqFgIBlAW8UF1ocgAERcViwx7aEiojZbHbfNiHfBBfRGAA00SsNmuyGOf3JyAgOHoBEpJHR2zAWMOkIAdBg4Fheu1oBMoiRpELAhswAYoCB1ptmRJEi87kMRoJxjjAjEbLCAFIZAAWIFhBMCcBYmoAzAAGQ2BUFgeh0UiUlGojV0WEAMWA-Qy1tRqJNmoAjFajX7JKHUc6XSS3agsBkwL6-cgA26AKxJkUkNhSFP0ZbNRgSRqFtZMnaHPlQAZKgUyS4ZPDsnAZFi9ctgOuEDvsjXsyGHADkOv1yAATIPuzKduzbfRSBa2L2Sf38VDkIPPd7x4OgA

[proper bridge]

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

bmkotu#7304

Playground Link

Preview:```ts
interface Simple {
[key: string]: string | Simple[]
}

interface ItemString {
value: string
name: string
}

interface ItemArray {
value: ItemString[]
name: string
}

interface Complex {
[key: string]: ItemString | Complex[]
}

const infer = (data: Simple): Compl
...```

You can choose specific lines to embed by selecting them before copying the link.

[proper bridge]

Burrito#6903

Playground Link

Preview:```ts
type Infer<T> = {
-readonly [K in keyof T]: T[K] extends string
? {name: K; value: string}
: Infer<T[K]>
}

declare const infer: <T>(data: T) => Infer<T>

const data = {
name: "John",
age: "30",
pets: [
{
name: "Fido",
age: "10",
...```

You can choose specific lines to embed by selecting them before copying the link.

[last dragon]

Do you want to do this recursively? Or just for the first layer?

If you want to do it for the first layer only: you can do something like this:

https://www.typescriptlang.org/play?#code/JYOwLgpgTgZghgYwgAgMrALYAcA2KDeAUMsgNoDWEAngFzIDOYUoA5gLp2PMgvIA+aTLgik2AbkIBfQoVCRYiFAElIGVE1bIiJAG5wcAVwicNPCSRBwMxhqZZSZc6PCTIAwgHtseAB5biZJS0ttzsdCoQanb87l7CPqIS0oRgVFgoAIJQUHBUAKJ41uAAPFk5VAB8yAC8yGW5yBA+kCAAJvTIABSgMNDIBZEQ4ACUosgA-P2FQ2DIdCAQOtAyqenIACoent5NxeuNzUPtgjtVtdqB1MigyEEeMBscGxTUbActx1yakxFRoXMbLZxXylbK5AZFMB7F5UNgVCqiByEBAeECMa4gXpQGrIPbvI4ddCnTqtOBgOB0dbDSlAnY+PZnKoXFFo2ZQCD0Aw4WbnSTIOAdTbbeIM8zIGAebGdFnooIY5Ck8nDfwkEgy2Z6QwoWqKuAw8QBEjAB6dVYQe7ITVGGrVWoAIi+PDtyouquQ7M53P1OPwlv0RgANMhLNY6HLJGKSHyIDh6ARDaqPVywN7alaIAA6DBwLDdTHQYaR5DSKMBdlgAxQEDujnJpIydUKskUk7CH0BEM2O0AKQ8AAsQHaAwE4CwuwBmAAMQ4C6TA9DopATrosVi7ADFgK0PDO3SRR12AIzT4duySn1Ur1eh5B21BYDxgXd7g90O0AVmfpZIbCk-I66oSMiqLokm3I4j00Aks2hYNiBHh4BmOAeCwnRgWAsGEOhGadhm6Y4gA5L2A7IAATARWG1tyGZzvQpCTmwOFrnh-rasgBGbtuZEEUAA

[proper bridge]

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

Niek#4887

Playground Link

Preview:```ts
interface Simple {
[key: string]: string | Simple[]
}

interface ItemString {
value: string
name: string
}

interface Complex {
[key: string]: ItemString | Complex[]
}

type ArrayElement<Array> =
Array extends (infer Element)[] ? Element : never
...```

You can choose specific lines to embed by selecting them before copying the link.

[last dragon]

It still contains some errors, but the idea is there

Also see this documentation page:

https://www.typescriptlang.org/docs/handbook/2/mapped-types.html

Ideally it should be recursive but one layer is fine too

[dire shard]

This one is recursive.

[last dragon]

thanks I will have a look at the code you posted

The type mapping I provided is recursive as well, yes. It doesn't support multiple different interfaces though. As long as it is just one class/interface, it should be fine

I see so the trick is to use the [key in keyof T] and use the ternary to check for the type it extends on inside the.. type

Exactly. This leaves the defined keys intact in the complex variant, and allows you to (recursively) map the strings to the complex strings and the simple arrays to complex arrays

I think I got it to work with an additional ternary https://www.typescriptlang.org/play?#code/JYOwLgpgTgZghgYwgAgJIGVgFsAOAbFAbwChlkBtAawgE8AuZAZzClAHMBdB51kN5AD5pMuAuQ6DkACh7tJGbPgjiAlOIDcxAL7FioSLEQpUAYQD2oiAA8AanDwBXIqWQA3e0+4t2msiDhYEF68bJo6xGA0OMbmllYAPAAqyNaQIAAmjMKKBAB8yAC8yCRk5ADSyKDI1DRmMMiJXA3lEqkQGVmyfC5kAPxosUq2HhA9yAyJLSlWaZnZluJj-aYWQ0kt5CAOWABG0By5i2RkDCAQrtBhmsQIZiDMlSAw0IXISdOzWQqWuVLpcGA4BMVAwVnEkvkCvkSshbvcwMgoBBGA48GAGHAQDRXoQtL5kDAzFBpHCHjVHsh-oCVMUxqSEe5HCgilS4FRaBx8WRgPUpJFonU3CNCgUigAiLpsMU0mHHRHI1Fgdk0CRFQhCpkAGmQ-kCDHJeLGWhSeEYzjlZCRKLRytVGqcADosHAcFIpMBIFgaVDHs8oO7PSoVFzkDoyGH5WAHFAQPLrQi4F9BgQEolclddPTKQC4DiXLqgsgxQApMwACxAYs1LjgbELYoAzAAGKsuaJgRgMchjWXHAsMMUAMWA6TMrYtyFr9YAjC3q3KtPPjr2-AF6+gcGYwOOLVOBwBWHfhpccauGrNWxWvUB+v454OZu6MMwEB14MxsKSXtEP4jfsAOgWDqMk46jIAA9OBTBlmYqLpMgADuRKUH+Cpog67aMOQTYcIBa7ASMYGQdBsF4PBSFQCh-4YRAHZ4YE9EQERUGMDBcE6luiHIcQQA

[proper bridge]

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

bmkotu#7304

Playground Link

Preview:```ts
interface ISimple {
[key: string]:
| string
| ISimple[]
| (string | ISimple[])[]
}

interface IComplexValue {
value: string
name: string
}

type IComplex<T extends ISimple> = {
[K in keyof T]: T[K] extends string
? IComplexValue
: T[K] extends ISimple
...```

You can choose specific lines to embed by selecting them before copying the link.

[last dragon]

With a bit of trickery to make sure mapping over the array works as well

now I want to the
interface ISimple {
[key: string]: string

not to just be a string but instead a "BaseType" like:
type BaseType = string | number | boolean | null | undefined;

but will this work in the ternary check?

It should yeah

Small word of warning though: I see you use infer as a variable name. This is technically allowed, but it is also a reserved word for use inside types

I try to avoid them in code

right yes thanks, it was just for the example 👍

Np. Good luck 🙂

Thanks, I got that to work too 😄
I will leave the final code here in case it can help someone else:

https://www.typescriptlang.org/play?#code/C4TwDgpgBAQghgZwgFXNAvFBwBOBLAOwHMoAfKAgVwFsAjCHMqWgexYBsI4Cmr32mlAgBMIAM0IRhAbgBQswsAZi4AY2gBJAMp5qYTlADesqFADaAawggAXFlyEiAXTvwkqSE2279EM06YACjcUNC8dPU5-AEp-OQBfeUVlNU0AYRZIiAAPADU4dkoIAB5kKBylEQRYRFDIAD4jEygANwKiu2Q5UwI4agg7bHxiBPlQTw0MrOzS8uzK4WrvLMbMY1MzAGkoQigrEBYxKGQXY62Aiogqmvc0ZtMAfihJzN889pLkc-r7qE7zuYLJYRXz+X5PF7TUrnMxUOgMJz1MGmUx2AgQFoMBJyVQsAjYHYEMQMKCYWaXa7LXz1QLCODAOCdaJ2SFvUqrRrrKC4-HAKA4CAISjsYB2bggUlGeLdKBiFiMQI8gn7QlQOkM6JNFHcvEEtqFDBq+lwSzWJwy0x4I6BcYQQ6tD5QACE6EwACIWLQAFYQVTAN2arnagVCkWmkABNYOg0AGgofQGe2sUGlv3i5XYSC12v5guFwHDkejRQeADpqHAwIFAnglNRNehGoRiTga3XotELSnmolTALgJQcDwQ-moIhnlM2ch6tj5Eq+eq4JKub1+nY3QApFgACwIbpjzTgRETAGYAAwH0zbxBb2h2XBFS9QL2etHC9hPyDABB2My-IMoquiZugAYngwgsPuvymEeiYAIwXmmT6mABPQJuuWhgCw-rISisF2AArLh8RPk4B6pvOuahnymDNgwtLGp2c66hwECluwLBEIEI4ikxsg8cApZAaW+pFNIUAAPQSVg24sMKwhQAA7vKFj8XmIqlrBImOlJMlyewCkENhSkqWp1Gll+CBmGeThCQm2kGuJukILJ8kmTgqkCRZEDfg5YmSdJLn6YZxnKR5shAA