Need some help finishing off a generic object.map function, my current implementation is both extremely slow on the compiler to the point where it breaks (but works) and currently i can't think of a good way to infer the ReturnType
type DeepKeyOf<T extends object> = {
[K in keyof T]: T[K] extends object ? DeepKeyOf<T[K]> | { key: K; value: T[K] } : { key: K; value: T[K] }
}[keyof T];
function objectMap<T extends object, B>(obj: T, mapper: (value: DeepKeyOf<T>) => any): T {
return Object.keys(obj).reduce((newObj, key) => {
return { ...newObj, [key]: mapper(obj[key]) };
}, {}) as any;
}
This will give back a discriminated union of {key, value} object literal pairs such that you can check the key with key === "foo" and get the typeguarded value of that key back which is what i want.
2 problems.
If someone says they can solve the problem with higher-kinded types give me the pseudo code perferably with scala syntax for HKT"s and i can write out a implementation that should finish it off.
EDIT:
type DeepKeyOf<T extends object> = {
[K in keyof T]: T[K] extends object ? DeepKeyOf<T[K]> | { key: K; value: T[K] } : { key: K; value: T[K] }
}[keyof T];
interface IPerson {
name: "susan";
children: {
billy: string;
sally: Date;
};
}
will give back {key: "name", value: "susan"} | {key: "children", value: {billy: string, sally: Date} | {key: "billy", value: string} | {key: "sally", value: Date}
{key: "name", value: "susan"} | {key: "children", value: {billy: string, sally: Date} | {key: "billy", value: string} | {key: "sally", value: Date}
EDIT: This is how far iv'e gotten which is close, but it only works when all keys are handled individually if you remove the "if key == "dob"" the ReturnType comes out as not what i want because Dob is a union of the other types.
// also i went with just making it shallow object.map to make it easier on the compiler and myself.
export type UnionToIntersection<U> = (U extends any ? (k: U) => void : never) extends ((k: infer I) => void)
? I
: never;
type Omit<T, K extends keyof T> = Pick<T, Exclude<keyof T, K>>;
type ShallowKeyOf<T extends object> = { [K in keyof T]: { key: K; value: T[K] } }[keyof T];
interface IPerson {
name: "susan";
children: {
billy: number;
sally: Date;
};
dob: Date;
}
type GenerateRecord<Tuple extends [any, any]> = Tuple extends infer SELF
? SELF extends [infer K, infer V] ? (K extends string ? Record<K, V> : never) : never
: never;
type ChangeValue<T extends object, Tuple extends [keyof T, any]> = Omit<T, Tuple[0]> extends infer SELF
? SELF & UnionToIntersection<GenerateRecord<Tuple>>
: never;
function objectMap<T extends object, TupleReturn extends [keyof T & string, any]>(
obj: T,
mapper: (value: ShallowKeyOf<T>) => TupleReturn
): ChangeValue<T, TupleReturn> {
return Object.keys(obj).reduce((newObj, key) => {
return { ...newObj, [key]: mapper((obj as any)[key]) };
}, {}) as any;
}
const test = objectMap(("" as any) as IPerson, ({ key, value }) => {
if (key === "name") {
return [key, new Date()];
}
if (key === "dob") {
return [key, "NOW STRING"]
}
return [key, new Date()];
});
Here is an approach I take by breaking apart the object-ey keys and non-object-ey keys. I think its a much wider type space to extend object
, and it typically gives me a hard time because it includes things like Dates.
type NonObject = Date | RegExp | string | number;
type ObjectValuedKeys<T> = {
[K in keyof T]: T[K] extends NonObject ?
never :
{ o: K }
}[keyof T]['o'];
type NonObjectValuedKeys<T> = {
[K in keyof T]: T[K] extends NonObject ?
{ o: K } :
never
}[keyof T]['o'];
type NonObjectKeyValues<T> = {
[K in NonObjectValuedKeys<T>]: {
key: K;
value: T[K];
}
}[NonObjectValuedKeys<T>];
type ObjectKeyValues<T> = {
[K in ObjectValuedKeys<T>]: MapKeys<T[K]>
}[ObjectValuedKeys<T>];
type MapKeys<T> =
{
v: NonObjectKeyValues<T>,
k: ObjectKeyValues<T>;
}['v' | 'k'];
interface IPerson {
name: 'susan';
children: {
billy: string;
sally: Date;
deeper: {
norma: RegExp,
}
};
}
MapKeys<IPerson>
gives me
{
key: "name";
value: "susan";
} | {
key: "billy";
value: string;
} | {
key: "sally";
value: Date;
} | {
key: "norma";
value: RegExp;
}
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