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Added an example from DataBrain

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ajeffrey@roblox.com 2022-01-06 16:52:16 -06:00
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21
rfcs/recursive-type-unrestriction.md
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@ -20,7 +20,26 @@ but *not* recursive type functions, such as:
type TreeWithMap<a> = { ..., map: <b>(a -> b) -> Tree<b> }
```
These examples come up naturally in OO code bases with generic types.
These examples come up naturally in OO code bases with generic types, for example
```lua
--!strict
export type PromiseFor<T> = {
andThen: <U>(
self: PromiseFor<T>,
onFulfilled: ((result: T) -> U)?,
onRejected: ((err: string) -> U)?
) -> PromiseFor<U>,
catch: <U>(
self: PromiseFor<T>,
onRejected: ((err: string) -> U)?
) -> PromiseFor<U>,
finally: <U>(
self: PromiseFor<T>,
onResolvedOrRejected: ((wasFulfilled: boolean, resultOrErr: T | string) -> U)
) -> PromiseFor<U>,
}
```
as discussed at the [Roblox DevForum](https://devforum.roblox.com/t/regression-with-genericrecursively-defined-types/1616647).
## Design