我正准备使用 fp-ts
学习函数式编程,我只是在问自己,将这样的东西“转换”为函数式范式的正确函数式方法是什么:
//OOP:
interface Item {
name: string;
}
class X {
private readonly items: { [s:string]: Item[] } = {};
add(i: Item): Item {
if(!this.items.hasOwnProperty(i.name))
this.items[i.name] = [];
if(this.items[i.name].indexOf(i) < 0)
this.items[i.name].push(i);
return i;
}
}
所以,我想我应该这样做:
import * as O from 'fp-ts/es6/Option';
import * as E from 'fp-ts/es6/Either';
// using interfaces from above
interface state {
items: { [s:string]: Item[] }
}
export const createState = (): State => ({ items: {} });
export const add = (s: State, i: Item) => pipe(
// using IO here?
E.fromPredicate(
() => s.hasOwnProperty(i.name),
() => []
)
)
// to use it:
import { createState, add } from './fx';
let state = createState();
// update
state = add(state, {name: 'foo'})
既然add()
操作涉及到state的修改,是不是应该依赖IO
?如果 add
返回一个新的状态对象,它是一个纯函数,所以它不需要使用 IO?所以我在这里提出的问题可能有点宽泛,但是:这里推荐的技术/模式是什么?
最佳答案
Since the add() operation involves the modification of state, should it rely on IO?
是的,add() 不会返回任何内容,但具有状态效果,因此它应该返回 IO<void>
If add returns a new state object, it is a pure function, so it wouldn't need to use IO?
正确。
What are the recommended techniques/pattern here?
函数式程序员通常不惜一切代价避免可变状态。
您要实现的是写时复制多重映射。您不需要 fp-ts
中的任何内容为此。
type MyItem = { name: string };
// we've made the store polymorphic
type MyObj<Item> = { [s: string]: Item[] };
// this is only necessary if you want to expose an implementation-independent api.
export const empty = {};
// i before o, in case we want currying later, o will change more.
const add = <Item>(k: string, v: Item, o: MyObj<Item>) =>
// abuse the spread operator to get create a new object, and a new array
({ ...o, [k]: [v, ...(o[k] || [])] });
// specialization for your item's case
export const addMyItem = (i: MyItem, o: MyObj<MyItem>) => add(i.name, i, o);
然后你可以这样做:
const a = addMyItem({ name: "test" }, addMyItem({ name: "test" }, empty));
关于typescript - OO 到函数式——从日常问题中学习,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/65714555/