[jaen]

`Readonly<T>` in TypeScript is almost useless, unsound and completely unsafe (as are most other things in TypeScript), and in no way equivalent to the Rust affine type system.

In particular, Readonly only prevents writing to the immediate fields of the object, but doing eg `const x: Readonly<X>; x.a.b = ...` is completely fine (ie. nested mutability is allowed). If you want transitive immutability, you need a type-level function (such as `ReadonlyDeep` from `type-fest`), but then that gives terrible error messages.

Also due to the bivariance of the TypeScript type system, using Readonly in combination with generics can silently and automatically cast it away, making it largely pointless for actual safety...