Generic inference by argument

[cinder condor]

How can I make this generic type inference work?
https://www.typescriptlang.org/play?target=99#code/C4TwDgpgBA0hIFkCGYA8AVAogO2AS1AD4oBeKAbwCgooBtOEKPbKAa3gHsAzKLXAkAF0A-AC4oAZ2AAnZgHMA3JQC+SyhAAeYDtOBRQkKMjCQAJjnygMFgQBpeDY1E3AI2UxNjxj1-kWJkVACQ9PBMLOwg3Lw2oFBInuiOKKFCzhqu7p5SsthyUMIO3ikMglDipeJ8liCpgkqqlJRcAK7YAMb4HCzMAG4Q0hIQyWjVdlDt3VJFiCjpmR5es6OxIISEABSRxlUjAJSUwdIQwC3SLADyAEYAVhCdAHRc0hwAthayEBIblEFB13dHm4ZHgvltimA9g9XigNkhSMQkA9jv1BhANnsDkE9vFPCNUMYzKtfDV7EkIesGk0DNAAKpDaSkCi-PCmcTYFqvK4DJRBCAwvAAG3EOXkvK4eEGwAAckhXhARSC8g01AB6VVQADCCWgAEYoBtpEgAO7xaRyTnAg7qqCYLT3fB5fQccJcAYzJwJJjAADknjACSGpnClEm2GmfQGQ3pAxG9PkACUTQBBc2W3BMyNo-Ex6SbYKs8QAIgAkgARIu2X4SqWy+XFmtSAD62DlECLKj2ao12qGUAATAbekhZEgroLoCOLfLcAcw9MWgyRkyC2yoKWK1Wgo2ZW2G5Lm635R3lLiJlNgN3bfbOvJna73eTlmeCH6oAGJEGQ-O9Fno0uIUzbBUSGHMGU2RdYwhLtKCAA

[thick sand]

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

Dec#1697

Playground Link

Preview:```ts
type KeyMap<TEntity> = {
[Key in keyof TEntity]?: string;
};

export type MappedEntity<TEntity, TKeyMap extends KeyMap<TEntity>> = {
[Key in keyof TEntity as TKeyMap[Key] extends string ? TKeyMap[Key] : Key]: TEntity[Key];
};

function inverseKeyMap<TEntity, const TKeyMap extends KeyMap<TEntity>>(keyMap: TKeyMap)
...```

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

[toxic pier]

You can't have a set of type params where some are inferred and some are manually specified

https://github.com/microsoft/TypeScript/issues/10571

[cinder condor]

that seems pretty silly sigh cheers, was hoping there was a way around it

seems annoying as it has the type via the argument

which makes that second case impossible as I'd have to somehow get the typeof it

[green moat]

you can somewhat-goofily split it into two parameter lists using a higher-order function:

[thick sand]

mkantor#7432

Playground Link

Preview:```ts
type KeyMap<TEntity> = {
[Key in keyof TEntity]?: string;
};

export type MappedEntity<TEntity, TKeyMap extends KeyMap<TEntity>> = {
[Key in keyof TEntity as TKeyMap[Key] extends string ? TKeyMap[Key] : Key]: TEntity[Key];
};

const inverseKeyMap = <TEntity>() => <const TKeyMap extends KeyMap<TEntity>>(keyMap: TKeyMap) =>
...```

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

[cinder condor]

I was thinking that would be the case - a bit annoying but ah well, cheers