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Description
When using the mixin pattern, there are 2 main notations to define the type of the mixin entity.
The mixin pattern:
export type AnyFunction<A = any> = (...input : any[]) => A
export type AnyConstructor<A = object> = new (...input : any[]) => A
export type Mixin<T extends AnyFunction> = InstanceType<ReturnType<T>>
export const Box = <T extends AnyConstructor<object>>(base : T) =>
class Box extends base {
value : any
}1st notation:
export type Box = Mixin<typeof Box> {}2nd notation:
export interface Box extends Mixin<typeof Box> {}The 1st notation can not be used for recursive definitions (#29872). Because of that we primarily use 2nd notation. It works fine in most cases, however I found a case, when it produces invalid type error. The full snippet to reproduce the problem below.
Note:
- The typechecker correctly figures out that there's no
zxcproperty onthis, inside theobservemethod ofQuarkmixin. - In that method, it does not complain about the
this.valueusage - It does complain, when
valueis used on function argument - If you'll switch the
Quarkmixin to the 1st notation, the error will disappear
Expected behavior:
- No type errors for the definition of
testfunction below
export type AnyFunction<A = any> = (...input : any[]) => A
export type AnyConstructor<A = object> = new (...input : any[]) => A
export type Mixin<T extends AnyFunction> = InstanceType<ReturnType<T>>
export const Box = <T extends AnyConstructor<object>>(base : T) =>
class Box extends base {
value : any
}
export interface Box extends Mixin<typeof Box> {}
export const Observable = <T extends AnyConstructor<object>>(base : T) =>
class Observable extends base {
observe () : Quark {
return
}
}
export interface Observable extends Mixin<typeof Observable> {}
export const Quark = <T extends AnyConstructor<Box & Observable>>(base : T) =>
class Quark extends base {
observe () : Quark {
// No error here!
this.value
// error: Error:(28, 14) TS2339: Property 'zxc' does not exist on type 'Quark'.
this.zxc
return
}
}
export interface Quark extends Mixin<typeof Quark> {}
const test = (a : Quark) => a.value // <-- Error:(35, 28) TS2339: Property 'value' does not exist on type 'Quark'.Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment