Type inference does not work when in return position

[jerguslejko]

TypeScript Version: 3.7-beta

Search Terms: inference, generic functions

Code

export function foo<T, K>(props: {
    seed: T;

    producer: (x: T) => K;

    consumer: (data: K) => void;
}) {
    //
}

foo({
    seed: "foo",

    producer: (seed) => {
        // type of `seed` is string
        return seed; 
    },

    consumer: (data) => {
        // type of `data` is unknown 
    }
})

Expected behavior: TypeScript infers K to a string, so the type of data is string.

Actual behavior: data variable is unknown.

[AnyhowStep]

I believe this is also because TS cannot perform inference on the same object multiple times?
#34865

It is why I use the builder pattern.
The builder pattern lets me break apart inference on one giant object into multiple inferences on multiple smaller objects/values
#34907

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.

[jerguslejko]

@AnyhowStep is took me 2 months exactly to understand what you mean :))

I'm able to reproduce this behaviour by swapping from f({ a, b }) to f(a, b). The non-object version works correctly. However, I'm trying to type a TSX component which always receives an object.

I think I'm out of luck :(

Thank you though! I learned something