Functions from Ramda about fxts

[gabriel-ss]

@ppeeou indeed pluck would work in the example I gave. I chose it for its simplicity but perhaps it wasn't the best choice; the places where these two show up in our codebase are closer to something like:

type Item = string

const defaultItemPage = { itemsPage: [] as Item[], currentPage: 1, totalOfPages: 1 }

type ItemPage = typeof defaultItemPage;

const fetchItemsPage = (pageNumber: number) => {
    const response = fetch(`/itemsPage/${pageNumber}`).then(r => r.json()).catch(always(defaultItemPage))

    itemsProxy.itemsPage = response.then(prop("itemsPage"))
    itemsProxy.currentPage = response.then(prop("currentPage"))
    itemsProxy.totalOfPages = response.then(prop("totalOfPages"))
};

I see that you opened #201; thanks for taking the time to address this issue! I opened #202 adding some other functions, but I also included an implementation suggestion of prop because type inference on #201 failed for me in some cases. More specifically

const objs = [{ key: "value" } as const, { key: "not value" } as const, null];

const obj1 = prop("key", { key: "value" } as const);
const obj2 = prop("key")({ key: "value" } as const);
const obj3 = prop("key", null);
const obj4 = prop("key")(null);
const obj5 = prop("key", objs[1]);
const obj6 = prop("key")(objs[1]);

makes typescript complain of objects from 2 to 6. Feel free to use or modify it if you want!

[gabriel-ss]

4.9.5 from the environment too; more precisely, with

gabriel@desktop ~/Projects/fxts (git)-[main] % npm exec tsc -- --version
Version 4.9.5

and

/**
 *
 * Returns a function that when supplied an object returns the indicated property of that object, if it exists.
 *
 * @example
 * ```ts
 * const arr = [1, 2, 3, 4, 5];
 * const n = prop(0, arr); // number
 *
 * const obj = {a: "1", b: 2};
 * const s = prop('a', obj); // string
 * const n = prop('b', obj); // number
 *
 * pipe(
 *  [{name:"foo", value: "bar"}, {name:"foo2", value: "bar2"}],
 *  map(prop('name')),
 *  toArray,
 * ); // ["foo", "foo2"]
 * ```
 */
export function prop<O extends object, K extends keyof O>(
  a: K,
): (obj: O) => O[K];

export function prop<O extends object, K extends keyof O>(a: K, obj: O): O[K];

export function prop<O extends object, K extends keyof O>(a: K, obj?: O): any {
  if (obj === undefined) {
    return (obj2: O): O[K] => {
      return obj2[a];
    };
  }

  return obj[a];
}

export default prop;

const objs = [{ key: "value" } as const, { key: "not value" } as const, null];

const obj1 = prop("key", { key: "value" } as const);
const obj2 = prop("key")({ key: "value" } as const);
const obj3 = prop("key", null);
const obj4 = prop("key")(null);
const obj5 = prop("key", objs[1]);
const obj6 = prop("key")(objs[1]);

I get

gabriel@desktop ~/Projects/fxts (git)-[main] % npm run compile:check    

> @fxts/[email protected] compile:check
> tsc --project tsconfig.json

src/prop.ts:42:19 - error TS2345: Argument of type 'string' is not assignable to parameter of type 'never'.

42 const obj2 = prop("key")({ key: "value" } as const);
                     ~~~~~

src/prop.ts:43:19 - error TS2345: Argument of type 'string' is not assignable to parameter of type 'never'.

43 const obj3 = prop("key", null);
                     ~~~~~

src/prop.ts:44:19 - error TS2345: Argument of type 'string' is not assignable to parameter of type 'never'.

44 const obj4 = prop("key")(null);
                     ~~~~~

src/prop.ts:44:26 - error TS2345: Argument of type 'null' is not assignable to parameter of type 'object'.

44 const obj4 = prop("key")(null);
                            ~~~~

src/prop.ts:45:19 - error TS2345: Argument of type 'string' is not assignable to parameter of type 'never'.

45 const obj5 = prop("key", objs[1]);
                     ~~~~~

src/prop.ts:46:19 - error TS2345: Argument of type 'string' is not assignable to parameter of type 'never'.

46 const obj6 = prop("key")(objs[1]);
                     ~~~~~

src/prop.ts:46:26 - error TS2345: Argument of type '{ readonly key: "value"; } | { readonly key: "not value"; } | null' is not assignable to parameter of type 'object'.
  Type 'null' is not assignable to type 'object'.

46 const obj6 = prop("key")(objs[1]);
                            ~~~~~~~


Found 7 errors in the same file, starting at: src/prop.ts:42

[ppeeou]

@gabriel-ss Thanks for your interest, we will review it :)

[ppeeou]

@gabriel-ss we will support prop but you can use this https://fxts.dev/docs/pluck before
it might be the feature you want

[ppeeou]

Can you tell me what version of typescript it complained about?
In my current environment (fxts, typescript 4.9.5) this seems to be reasonably inferred.

const { checks, check } = Test;

const objs = [{ key: "value" } as const, { key: "not value" } as const, null];
const obj1 = prop("key", { key: "value" } as const);
const obj2 = prop("key")({ key: "value" } as const);
const obj3 = prop("key", null);
const obj4 = prop("key")(null);
const obj5 = prop("key", objs[1]);
const obj6 = prop("key")(objs[1]);

checks([
  check<typeof obj1, "value", Test.Pass>(),
  check<typeof obj2, "value", Test.Pass>(),
  check<typeof obj3, undefined, Test.Pass>(),
  check<typeof obj4, undefined, Test.Pass>(),
  check<typeof obj5, "value" | "not value" | undefined, Test.Pass>(),
  check<typeof obj6, "value" | "not value" | undefined, Test.Pass>(),
]);

[ppeeou]

oh... you are right. your pr looks good better

[ppeeou]

release https://github.com/marpple/FxTS/releases/tag/v0.15.0