Add generic Deep type

[krzkaczor]

Is it possible to create generic Deep type that would minimize repetition between DeepPartial, DeepReadonly etc ?

[Andarist]

Was thinking about it a little bit and I think this aint possible - although Im quite new to TS so I might miss something.

The challenge here is that each of those types does something different to property modifiers, and also we don't know how to map a property modifier to array modifier. So at the very least we would require 3 type parameters <RecursiveMapper, ObjectHandler, ArrayHandler> which seems more than convoluted and I still don't know how to apply ObjectHandler to the transformation.

[Beraliv]

You want to have high order function in TypeScript (which is discussed here – microsoft/TypeScript#1213)

You still can define Replace and change one type with another:

declare const __placeholder__: unique symbol;

type Placeholder = { readonly [__placeholder__]: unknown };

type Replace<T, X, Y> = {
  [K in keyof T]: T[K] extends X ? Y : T[K];
};

But let me check that it can be implemented somehow

Also it has limitations with restrictions but we don't have them so might be possible

[Beraliv]

Replace has a lot of limitations, e.g.

1. It isn't working if you don't know element types in advance – https://tsplay.dev/W4pbXW
2. Can use Replace for one type of parameter, but if you have multiple placeholders, you need to have more and follow it really carefully
3. You can Replace only on first level, or implement a deep replacement (might be difficult)

Also, you might need several implementation of Replace: for objects and primitives

[Beraliv]

Several days ago I've seen work on hotscript - https://github.com/gvergnaud/hotscript

Maybe it will be possible to organise it so it would be possible to reuse the same types, although I didn't have a chance to play with it

[Beraliv]

I've closed the PR because it is not a priority right now, I may come back to it at some point