How to test if two types are exactly the same

Question

Here is my first attempt: (playground link)

/** Trigger a compiler error when a value is _not_ an exact type. */
declare const exactType: 

        

Answer 1

edit: The most refined version can be found here

Here's the most robust solution I've found thus far:

// prettier-ignore
type Exact = (() => T extends A ? 1 : 0) extends (() => T extends B ? 1 : 0)
    ? (A extends B ? (B extends A ? unknown : never) : never)
    : never

/** Fails when `actual` and `expected` have different types. */
declare const exactType: (
    actual: Actual & Exact,
    expected: Expected & Exact
) => Expected

Thanks to @jcalz for pointing in the right direction!