Typescript add only some type parameters

I would like to do this:

function foo<A, K extends keyof A>(a: A, key: K): A[K] {
    return a[key];
}

foo<Type>({ key: 'value' }, 'key');

But this doesn't work because ts requires all or none of generic types to be explicitly typed.

My workaround:

function bar<A>() {
    return {
        foo<K extends keyof A>(a: A, key: K): A[K] {
            return a[key];
        },
    };
}

bar<Type>().foo({ key: 'value' }, 'key');

Here the K type is implicit.

Now my question is, have any of you had the same problem and how did you solve it?

https://github.com/microsoft/TypeScript/issues/26242

I found this proposal on github which would make type parameters optional if possible. This has been open for a while though, in the mean time I'd still like to know your workarounds.

In fact, you don't need to write Type, typescript will try to infer the type of A, like

function foo<A, K extends keyof A>(a: A, key: K): A[K] {
    return a[key];
}

foo( { key: "value" }, "key" );

interface Bar {
    name: string;
    age: number;
    address: string;
}

const bar: Bar = {
    name: "tim",
    age: 18,
    address: ""
};

// It can also get the correct type
foo( bar, "name" );

TS playground