effector-multitarget-ending.ts

type Tuple<T = unknown> = [T] | T[]

type Tail<A extends Tuple> = 
    ((...args: A) => any) extends ((h: any, ...t: infer T) => any) ? T : never

type HandleVoidAnyUnknown<Target, Fallback> = [void] extends [Target /* void/any/unknown */]
    ? Fallback
    : Target

type StrictestFromTwo<L, R> =
    [L] extends [R]
        ? [R] extends [L]
            ? L // L = R
            : L // R > L
        : [R] extends [L]
            ? R // L > R
            : never  // L != R

type v = void
type s = string
type b = boolean
type n = number
type sn = s | n
type sb = s | b
type nb = n | b
type snb = s | n | b

declare const strictestTarget: unique symbol

type FindStrictest<T extends Tuple, U = T[0]> = (
    T['length'] extends 0
        ? {
            [strictestTarget]: U
        }
        : {
        [strictestTarget]:
            FindStrictest<
                Tail<T>,
                StrictestFromTwo<
                    HandleVoidAnyUnknown<U, T[0]>,
                    HandleVoidAnyUnknown<T[0], U>
                >
            >
        }
) extends { [strictestTarget]: infer Result } ? HandleVoidAnyUnknown<Result, any> : never

type Result01 = FindStrictest<[s]> // s
type Result02 = FindStrictest<[s, n]> // never
type Result03 = FindStrictest<[n, s]> // never
type Result04 = FindStrictest<[s, sn]> // s
type Result05 = FindStrictest<[sn, s]> // s
type Result06 = FindStrictest<[s, sn, snb]> // s
type Result07 = FindStrictest<[snb, sn, s]> // s
type Result08 = FindStrictest<[b, snb, sn, s]> // never
type Result09 = FindStrictest<[snb, sn, s, b]> // never
type Result10 = FindStrictest<[v]> // any
type Result11 = FindStrictest<[v, s]> // s
type Result12 = FindStrictest<[s, v]> // s
type Result13 = FindStrictest<[s, sn, snb, v]> // s
type Result14 = FindStrictest<[v, snb, sn, s]> // s
type Result15 = FindStrictest<[v, b, snb, sn, s]> // never
type Result16 = FindStrictest<[snb, sn, s, b, v]> // never