What does the following type implement and what is it useful for? type Opaque = T & { readonly __brand: Brand }; type UserId = Opaque; type ProductId = Opaque;

Explanation

The type Opaque with a __brand property creates a nominal typing simulation, ensuring UserId and ProductId are distinct despite both being strings. This prevents them from being interchangeable at runtime.

Key points

Opaque type with __brand enforces nominal typing
UserId and ProductId are distinct despite being strings
Prevents accidental interchangeability at runtime
__brand property adds unique identity to the types

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