IsEqual

In this medium-level challenge, you'll implement the type-level equal operator that returns a boolean for whether two given types are exactly equal.

Detailed Explanation

The naive approach using mutual extends fails for edge cases like any. The robust solution uses a function-type trick that leverages TypeScript's internal type comparison.

type IsEqual<X, Y> =
  (<T>() => T extends X ? 1 : 2) extends
  (<T>() => T extends Y ? 1 : 2)
    ? true
    : false

How it works:

• We create two generic function types <T>() => T extends X ? 1 : 2 and <T>() => T extends Y ? 1 : 2
• TypeScript compares these function types structurally, which requires X and Y to be identical for the conditional return types to match
• If the two function types are assignable to each other, X and Y are exactly equal and we return true
• This approach correctly handles edge cases like any, never, union types, and intersection types where simpler mutual-extends checks would fail

This challenge helps you understand TypeScript's type identity semantics and how to apply this concept in real-world scenarios.