const foo = (x: { y: number }) => {
    x.y = 42
}

const bar: { y: 0 } = { y: 0 }
foo(bar)

switch (bar.y) {
    case 0:
        console.log("always");
        break;
    default:
        const baz: never = bar.y;
        console.log("never", baz);
}

const coerceSetting = <T extends keyof IServerSettings>(
  key: T,
  value: string
): IServerSettings[T] | undefined => {
  if (key === "dmHelp") {
    const num = Number(value);
    if ([0, 1, 2, 3, 4].includes(num)) return num as IServerSettings[T];
  } else if (key === "reactRemovalTimeout") {
    const num = Number(value);
    // It's official, TypeScript is dumb. It won't compile *without* this cast.
    if (Object.is(num, -0)) return 0 as IServerSettings[T];
    if (Number.isFinite(num) && num >= 0) return num as IServerSettings[T];

interface IServerSettings {
  server: string;
  dmHelp: 0 | 1 | 2 | 3 | 4;
  reactRemovalTimeout: number;
}

function coerceSetting<T extends keyof IServerSettings>(
  key: T,
  value: string
): IServerSettings[T] | undefined
function coerceSetting(key: keyof IServerSettings, value: string): IServerSettings[keyof IServerSettings] | undefined {
}

  # Help string; can be object instead for embed. Object structure should match the EmbedData
  # interface. As of discord.js v14.0.3, this is intentionally undocumented (if you're on the
  # server, see the thread at discord.com/channels/222078108977594368/999317051782987797 ).
  # However, the interface is very similar to APIEmbed, which is documented at
  # discord-api-types.dev/api/discord-api-types-v10/interface/… .