variant-ts
v0.0.29
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Variant, Option and Result types for Typescript
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Variant-ts
Variant, Option and Result types for Typescript
Variants
import { Variant, variant } from "variant-ts";
type Connection =
| Variant<"IPV4", [number, number, number, number]>
| Variant<"IPV6", string>;
let ip = variant<Connection>("IPV4", [127, 0, 0, 1]);
Variants are very handy when used together with reducers:
import { Variant, variant, pattern } from "variant-ts";
import { match } form "ts-pattern";
type State = {
name: string,
age: number,
messages: string[]
}
type Action =
Variant<"ChangeName", string>
| Variant<"ChangeAge", number>
| Variant<"AddMessage", string>
function reducer(state: State, action: Action): State {
return match(action)
.with(pattern("ChangeName"), res => { return { name: res.val, ...state } })
.with(pattern("ChangeAge"), res => { return { age: res.val, ...state } })
.with(pattern("AddMessage"), res => { return { messages: [...state.messages, res.val], ...state } })
.exhaustive()
}
let initial_state = {
name: "John Doe",
age: 24,
messages: ["Hey, how are you?", "See you"]
}
let new_state = reducer(initial_state, variant<Action>("AddMessage", "Variants are awesome"))
Options
import { none, some } from "variant-ts";
const one = some("foo");
const two = none();
const three = one.map((x) => x.concat("bar"));
const four = two.map((x) => x.concat("bar"));
expect(three.val).to.equal("foobar");
expect(four.val).to.equal(undefined);
Results
import { err, ok } from "variant-ts";
const one = ok("foo");
const two = err("error");
const three = one.map((x) => x.concat("bar"));
const four = two.map((x) => x.concat("bar"));
expect(three.val).to.equal("foobar");
expect(four.val).to.equal("error");