How not to provide the keys for "deep" types every time?

[ProdigySim]

🍩 Feature Request

Is your feature request related to a problem?

No.

Describe the solution you'd like

type DeepOptional<O extends object, K extends Index = keyof O> = Optional<O, K, 'deep'>'

Using Object.Optional is very handy. But if you want to use the 'deep' option, it requires filling in the optional K parameter as well. For most cases where I want to use a deep-optional object, I'd like to use the default K = keyof T argument, so it's inconvenient to have to specify this parameter manually. Creating an alias for the 'deep' version of the command would allow people to leverage the nice defaults available.

Describe alternatives you've considered

I believe Typescript has discussed a feature where you could use _ in place of a generic parameter to accept the default value. This would let users write O.Optional<T, _, 'deep'> instead. However, I can no longer find the TS issue discussing this feature, so I don't know when or if it is expected to arrive.

Additionally, users could just create their own DeepOptional alias. But it has been nice to be able to consolidate many type aliases in a standard way under a single library like ts-toolbelt.

Teachability, Documentation, Adoption, Migration Strategy

We should be able to copy the documentation for Object.Optional, adding a note that this method is an alias for Object.Optional<O,K, 'deep'> and functionality is the same.

Examples

declare const mockItem: O.Optional<IItem, keyof IItem, 'deep'>;
// vs
declare const mockItem: O.DeepOptional<IItem>;

[millsp]

Hi @ProdigySim,

This is something that is not well documented, but you can do:

type test = O.Optional<IItem, any, 'deep'>;

Is that what you were looking for?

[ProdigySim]

Ah, that's definitely a lot better than having to duplicate the first type parameter. I think an alias could still be nice, but the any workaround does remove a lot of the need.

[millsp]

I'm marking this as resolved, as on of my goals is to provide a unified API for the type utilities (no duplicates). I feel like typing any is short enough not to create a new alias.

Cheers

[glen-84]

However, I can no longer find the TS issue discussing this feature

microsoft/TypeScript#26242