Issue with generic types on action

[tv1ster]

I have a:

2. Issue:

• Provide error messages including stacktrace

TypeScript error Type '{}' is not assignable to type 'number'.

• Provide a minimal sample reproduction. Create a reproduction based on this sandbox

Seems like generics for action not really working well. In real project I am triggering some simple action on rxjs subscription. But I created small example to show you the issue. I tried to duplicate your code for IActionFactory so it will be easier to understand the rootcause.

• Did you check this issue wasn't filed before?
• Elaborate on your issue. What behavior did you expect?

I expect TS to not throw error, because it have already all info about my types.

3. Idea:

• What problem would it solve for you?

For real, problem is not so huge, I just need to define some types for action, and TS will understand what is going on. But it would be great, if everything would work without strict types declaration.

• Do you think others will benefit from this change as well and it should in core package (see also mobx-utils)?
• Are you willing to (attempt) a PR yourself?

I found out, that issue will dissappear, if I will move generic types at top, like here, but I'm not sure about full impact of this change, so decided ask you about this issue. Maybe I'm doing something wrong? Because I'm not fully understand, why do we need these types

    <A1, R, T extends (a1: A1) => R>(fn: T): T & IAction
    <A1, A2, R, T extends (a1: A1, a2: A2) => R>(fn: T): T & IAction
    <A1, A2, A3, R, T extends (a1: A1, a2: A2, a3: A3) => R>(fn: T): T & IAction
    <A1, A2, A3, A4, R, T extends (a1: A1, a2: A2, a3: A3, a4: A4) => R>(fn: T): T & IAction
    <A1, A2, A3, A4, A5, R, T extends (a1: A1, a2: A2, a3: A3, a4: A4, a5: A5) => R>(fn: T): T &
        IAction
    <A1, A2, A3, A4, A5, A6, R, T extends (a1: A1, a2: A2, a3: A3, a4: A4, a6: A6) => R>(fn: T): T &
        IAction

while we can use only

<T extends Function>(fn: T): T & IAction

[tv1ster]

UPD. Also, seems like all this stuff

  <A1, A2, A3, A4, A5, A6, R, T extends (a1: A1, a2: A2, a3: A3, a4: A4, a6: A6) => R>(fn: T): T &
        IAction

can be refactored to

  <A extends any[], R, T extends (...A) => R>(fn: T): T & IAction

UPD.UPD. Seems like you have already discussed it here

[mweststrate]

Closing as duplicate

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