Narrow union type in function that spreads same property?

[steady parcel]

https://www.typescriptlang.org/play/?#code/C4TwDgpgBAcg9gEwgRigXigbygDwFxQDOwATgJYB2A5gDRQICGwDB2hDAthAcedXSB6lKVKAF9xAbgBQoSLEQQATOiy4hfWvSYs17LhpF0AXoerip02eGgBZEPCSrHKKAB8FSJTOkBjOBTEUBSKADaqABQUePYuAJQxDoroAHxQEZjSUNlQAHT5FDRZOYzMrMU5Ofm5FLmlDEWVlfrcUADkhBDAXG0V4tJicdJAA

Is it possible to narrow the type of n.data here?

[cerulean citrus]

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

andy.ray#0

Playground Link

Preview:```ts
type Node1 = {
x: string
data: {same: string; y: string}
}
type Node2 = {
x: string
data: {same: string; z: string}
}

type MyNode = Node1 | Node2

const nodel = (n: MyNode): MyNode => ({
...n,
data: {
...n.data,
same: "setme"
...```

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

[steady parcel]

Claude got something right for once!

const nodel = <T extends MyNode>(n: T): T => ({
    ...n,
    data: {
        ...n.data,
        same: 'setme'
    }
})

[drowsy hull]

@steady parcel are you able to change the types? if you rewrite MyNode like this (which is equivalent in terms of allowed values) it works:

[cerulean citrus]

mkantor#0

Playground Link

Preview:```ts
type MyNode = {
x: string
data:
| {same: string; y: string}
| {same: string; z: string}
}

const nodel = (n: MyNode): MyNode => ({
...n,
data: {
...n.data,
same: "setme",
},
})```

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

[drowsy hull]

eh, this is kinda fishy. here's an example of why it's not safe:

[cerulean citrus]

mkantor#0

Playground Link

Preview:ts ... const mySpecificNode = { x: '', data: { same: 'some very specific string', y: '' }} as const const result = nodel(mySpecificNode) const sus: 'some very specific string' = result.data.same // this typechecks console.log(sus) // but the value is actually `'setme'` at runtime

[scenic snow]

This works

[cerulean citrus]

alpacadev#0

Playground Link

Preview:```ts
type Node1 = {
x: string
data: {same: string; y: string}
}
type Node2 = {
x: string
data: {same: string; z: string}
}

type MyNode = Node1 | Node2

const nodel = <T extends MyNode>(n: T): T => {
return {
...n,
data: {
...n.data,
same: "setme
...```

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

[drowsy hull]

that's the same as what they posted above (via Claude)

[scenic snow]

Ohh you're right, completely missed that between the colorful playground embeds :D