Closed
Description
Trying to give better types to the redux library. Came across this issue. The issue appears to be the reindexing via keyof A at the end.
TypeScript Version: 2.7.0-dev.201xxxxx
Code
type Actions = {
INCREMENT: { x: number }
DECREMENT: { y: string }
}
type Concrete = {[K in keyof Actions]: {type: K} & Actions[K] }[keyof Actions]
type Generic<A> = {[K in keyof A]: {type: K} & A[K] }[keyof A]
type GenericConcrete = Generic<Actions>Expected behavior:
Concrete and GenericConcrete have the same type
Actual behavior:
Concrete has the correct type
type Foo = ({
type: "INCREMENT";
} & {
x: number;
}) | ({
type: "DECREMENT";
} & {
y: string;
})GenericConcrete has the wrong type
type Foo = ({
type: "INCREMENT" | "DECREMENT";
} & {
x: number;
}) | ({
type: "INCREMENT" | "DECREMENT";
} & {
y: string;
})
Unless I'm missing some kind of constraint on A in the Generic case that Typescript is able to use in the concrete case to work out the types correctly?