Pick type can't use common key types such as string, like Omit type

[falsandtru]

I'm not sure why the Pick type has the keyof T constraint although the Omit type doesn't have.

TypeScript Version: 3.7.x-dev.20200107

Search Terms:

Code

const sym = Symbol();
class C {
    p = 0;
    [sym]: '';
}
type a = Pick<C, symbol>;
type b = Omit<C, string>;
type Structural<T> = Pick<T, string | number>;

Expected behavior:
pass

type Pick<T, K extends string | number | symbol> = { [P in Extract<keyof T, K>]: T[P]; };
type Omit<T, K extends string | number | symbol> = { [P in Exclude<keyof T, K>]: T[P]; }

Actual behavior:
Type 'symbol' does not satisfy the constraint 'unique symbol | "p"'.(2344)
Type 'string | number' does not satisfy the constraint 'keyof T'.
Type 'string' is not assignable to type 'keyof T'.(2344)

type Pick<T, K extends keyof T> = { [P in K]: T[P]; }
type Omit<T, K extends string | number | symbol> = { [P in Exclude<keyof T, K>]: T[P]; };

Playground Link: http://www.typescriptlang.org/play/index.html?ts=3.8.0-dev.20200107#code/MYewdgzgLgBBCeBbGBeGBlJAjEAbAFAJQDcAUMLgIYQQwDCMA3qTKzAA6owAMZbMAbQSIAugC4YAcklkAvqSjx2AUxiUuABQCWwANYAeOgBo42PAD4yilTCxcA8oi1RDJ6ACctYAOaWFS1XQodwBXYCgQ90pcfQAVc00dA1i3YK9vGAAfGDAQxCxld0sgA

Related Issues:

[IllusionMH]

Duplicate of #30825 and may other?

[falsandtru]

No. That issue suggested the stricter Omit type but conversely this issue suggests the looser Pick type.

[RyanCavanaugh]

We can't really change either of them after they've shipped. You're free to use your own definitions if you'd like.

[falsandtru]

@RyanCavanaugh However, this change seems to make no breaking changes because this change just looses the constraint, right? I want you to answer this point.

[falsandtru]

I can't find the actual problem this improvement makes.

[RyanCavanaugh]

People complained that the Exclude we added didn't have a similar constraint, so presumably we'd get similar complaints about removing an existing constraint.

[falsandtru]

...Do you complain the same thing as that people? Eventually, the current definitions of the Exclude and the Extract have been symmetry. Asymmetric features are a basic anti-pattern. Such features are hard to use. I can't find any relevant reason to hold the Pick type and the Omit type asymmetry.

[typescript-bot]

This issue has been marked as 'Question' and has seen no recent activity. It has been automatically closed for house-keeping purposes. If you're still waiting on a response, questions are usually better suited to stackoverflow.