Let’s assume there is a object definition:

type Obj = {
    i: number
    b: boolean
    s: string
}

I want to define a type which would allow me to pass property name and a callback which would expect single argument with exactly the same type as a property:

const a: FormatEntry = {
    accessor: 'b',
    formatter: (value: boolean) => value ? 'a' : 'b'
}

My best try to far

type FormatEntry<K extends keyof Obj> = {
    accessor: K,
    formatter: (value: Obj[K]) => string
}

But it gives me an error “Generic type ‘FormatEntry’ requires 1 type argument(s).(2314)” which I don’t understand – I would expect TS to infer the generic’s argument on its own

Sure, I can provide that argument:

const a: FormatEntry<'b'> = {
    accessor: 'b',
    formatter: (value: boolean) => value ? 'a' : 'b'
}

but it’s double work. What am I doing wrong?