TypeScript exhaustive compile-time checks with `never`

never.ts

//Play with it here: https://goo.gl/dH6DLj

class UnexpectedValueError {
    public readonly stack: string | undefined;
    public readonly message: string;

    constructor(value: never) {
        const error = new Error(`Unexpected value ${value}`);
        this.stack = error.stack;
        this.message = error.message;
    }
}

class Type1 {
}

class Type2 {
}

class Type3 {
}

//If `Type3` is added here code won't typecheck until instanceof check is added to `getClassTypeLabel`
type Type = Type1 | Type2;

function getClassTypeLabel(instance: Type): string {
    if (instance instanceof Type1) {
        return "Type 1";
    }
    if (instance instanceof Type2) {
        return "Type 2";
    }
    throw new UnexpectedValueError(instance);
}

//If `"type3"` is added here code won't typecheck until new case is added to `getValueTypeLabel`
type ValueType = "type1" | "type2"; 

function getValueTypeLabel(value: ValueType): string {
    switch (value) {
        case "type1":
            return "Type 1";

        case "type2":
            return "Type 2";

        default:
            throw new UnexpectedValueError(value);
    }
}