Unable to store and reuse result of user defined type guard function

[rssfrncs]

TypeScript Version: 2.9.1

Search Terms: caching type guard result

Code

type TChildrenFunc = () => string;
type TChildren = TChildrenFunc | string;

function isFunction(render: TChildren): render is TChildrenFunc {
  return typeof render === "function";
}

// render is of type TChildren
const cacheResult = isFunction(render);

// errors below
const test = cacheResult ? render() : render;

Expected behavior:

Same as in-lining the type guard call.

Actual behavior:

TypeScript is unable to infer the correct type.

Playground Link: https://codesandbox.io/s/30v146k811 Check Hello.tsx

Related Issues: Nope.

[hraban]

I just came here to post a similar bug:

function twostep(x: symbol | string) {
    const isSymbol = typeof x === "symbol";
    if (!isSymbol) {
        console.log(`Type of x is still string | symbol here: ${x}`);
    }
}

function onestep(x: symbol | string) {
    if (typeof x !== "symbol") {
        console.log(`Type of x is now just string: ${x}`);
    }
}

playground

[mhegazy]

Looks like a duplicate of #24865

[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.