Definition for 'enhance' function type

Question

Definition for 'enhance' function type

I am currently working on defining a type for the evolve function from Ramda. The official definition provided does not seem to be functioning correctly.

type Transformation<State> = {
  [Key in keyof State]: (x: State[Key]) => any
}

declare function evolve
  <State extends {}, Evolver extends Partial<Transformation<State>>>(evolver: Evolver, state: State):
  {[Key in keyof State]: Evolver[Key] extends (...args: any[]) => {} ? ReturnType<Evolver[Key]> : State[Key]}

I'm attempting to implement this within a generic function:

const foo = <State extends {a: string, b: string}>(state: State) => {
  const test = evolve({
    a: x => x,
    b: x => x
  }, state)
}

However, I encountered an error:

Argument of type '{ a: (x: State["a"]) => State["a"]; b: (x: State["b"]) => State["b"]; }' is not assignable to parameter of type 'Partial<Transformation<State>>'.(2345)

The reason behind this error is unclear to me, making it challenging to resolve.

typescript ramda.js

Answer 1

Answer №1

It appears that there were a few issues at play. To resolve them, I restructured the code by elevating Evolver into its own type alias, which also eliminates an index problem when trying to designate it as the second generic parameter. Additionally, I updated some return types to unknown to allow TypeScript to infer them within the evolver object.

type Transformation<T> = {
  [K in keyof T]: (x: T[K]) => unknown;
};

type Evolver<State> = Partial<Transformation<State>>;

declare function evolve<State extends { [key: string]: unknown }>(
  evolver: Evolver<State>,
  state: State
): {
  [Key in keyof State]: Evolver<State>[Key] extends (...args: any[]) => infer R
    ? R
    : State[Key];
};

const foo = (state: { a: string; b: string }) => {
  const test = evolve(
    {
      a: (x) => x,
      b: (x) => x,
    },
    state
  );
};

Answer 2

It appears that there were a few issues at play. To resolve them, I restructured the code by elevating Evolver into its own type alias, which also eliminates an index problem when trying to designate it as the second generic parameter. Additionally, I updated some return types to unknown to allow TypeScript to infer them within the evolver object.

type Transformation<T> = {
  [K in keyof T]: (x: T[K]) => unknown;
};

type Evolver<State> = Partial<Transformation<State>>;

declare function evolve<State extends { [key: string]: unknown }>(
  evolver: Evolver<State>,
  state: State
): {
  [Key in keyof State]: Evolver<State>[Key] extends (...args: any[]) => infer R
    ? R
    : State[Key];
};

const foo = (state: { a: string; b: string }) => {
  const test = evolve(
    {
      a: (x) => x,
      b: (x) => x,
    },
    state
  );
};

Definition for 'enhance' function type

Answer №1

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