Switchtag
Switch expression for typescript tagged unions.
import { switchTag } from "https://deno.land/x/switchtag/mod.ts"
import { assertEquals } from "https://deno.land/std/testing/asserts.ts"
export type R =
| { type: "ok"; value: number; otherTag: 1 }
| { type: "err"; error: string; otherTag: 2 }
const reqs: R[] = [
{ type: "ok", value: 1, otherTag: 1 },
{ type: "err", error: "error", otherTag: 2 },
]
const first = reqs.map((req) =>
switchTag("type")(req)({
ok: ({ value }) => `${value} ok`,
err: ({ error }) => `${error} err`,
})
)
const second = reqs.map((req) =>
switchTag("otherTag")(req)({
1: ({ value }) => `${value} ok`,
2: ({ error }) => `${error} err`,
})
)
Deno.test("Example in README works", () => {
assertEquals(first, ["1 ok", "error err"])
assertEquals(second, ["1 ok", "error err"])
})Should I use it?
No. Use ts-pattern instead.
Bench
cpu: AMD Ryzen 5 5600G with Radeon Graphics
runtime: deno 1.34.2 (x86_64-unknown-linux-gnu)
file:///home/scarf/repo/deno-packages/switchTag/benchmarks/befault_bench.ts
benchmark time (avg) (min … max) p75 p99 p995
------------------------------------------------------------------ -----------------------------
switchTag with default 3.42 ms/iter (3.09 ms … 6.49 ms) 3.28 ms 6.29 ms 6.49 ms
ts-pattern with default 3.65 ms/iter (3.3 ms … 5.81 ms) 3.74 ms 4.99 ms 5.81 ms
native switch with default 340.04 µs/iter (291.87 µs … 2 ms) 343.1 µs 703.6 µs 833.52 µs
summary
switchTag with default
10.07x slower than native switch with default
1.07x faster than ts-pattern with default
file:///home/scarf/repo/deno-packages/switchTag/benchmarks/exhaustive_bench.ts
benchmark time (avg) (min … max) p75 p99 p995
----------------------------------------------------- -----------------------------
switchTag 701.07 µs/iter (517.81 µs … 2.66 ms) 705.38 µs 1.63 ms 1.98 ms
ts-pattern 4.35 ms/iter (3.9 ms … 5.91 ms) 4.45 ms 5.74 ms 5.91 ms
native switch 381.61 µs/iter (306.95 µs … 2.75 ms) 381.49 µs 714.34 µs 852.12 µs
summary
switchTag
1.84x slower than native switch
6.21x faster than ts-patternLimitations
using otherwise cannot narrow types unlike to ts-pattern or native switch.