Combine index signature (of union of string literal type) with other keys

[mhchem]

TypeScript Version: 2.6.1

The Code I want to move to TS makes use several times of this (simplified) pattern:

let e = {
    a: 1,
    "b": 2,
    c: 3,
    get: (i) => e[i] + "."
}

Here is the same code annotated with types.

type Kinds = "a"|"b"|"c"

// This works.
type DObjects = {
    [key in Kinds]: number;
}
let d: DObjects = {
    a: 1,
    "b": 2,
    c: 3
}

// This does not work yet ...
type EObjects = {
    [key in Kinds]: number;
    get: { (i: Kinds): string };
}
let e: EObjects = {
    a: 1,
    "b": 2,
    c: 3,
    get: (i) => e[i] + "."
}

But this does not work, although this should be equivalent to

// ... but should be equivalent to this.
type FObjects = {
    a: number;
    b: number;
    c: number;
    get: { (i: Kinds): string };
}
let f: FObjects = {
    a: 1,
    "b": 2,
    c: 3,
    get: (i) => f[i] + "."
}

Expected behavior:

Treat [index in Kinds] (where Kinds is a union of string literal types) the same way as if one would type them explicitly.

Actual behavior:

issue.ts(16,5): error TS1005: '}' expected.
issue.ts(16,31): error TS1005: '=>' expected.
issue.ts(17,1): error TS1128: Declaration or statement expected.

[mhegazy]

type EObjects = {
        [key in Kinds]: number;
    } & {
        get: { (i: Kinds): string };
    };

[mhchem]

Wow! This should make it in the documentation.

[typescript-bot]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.