JavaScript のArray.concat関数を型システムに実装します。この型は 2 つの引数を受け取り、受け取ったイテレータの要素を順に含む新しい配列を返します。
例えば：
type Result = Concat<[1], [2]>; // expected to be [1, 2]
import type { Equal, Expect } from '@type-challenges/utils'
const tuple = [1] as const
type cases = [
Expect<Equal<Concat<[], []>, []>>,
Expect<Equal<Concat<[], [1]>, [1]>>,
Expect<Equal<Concat<typeof tuple, typeof tuple>, [1, 1]>>,
Expect<Equal<Concat<[1, 2], [3, 4]>, [1, 2, 3, 4]>>,
Expect<Equal<Concat<['1', 2, '3'], [false, boolean, '4']>, ['1', 2, '3', false, boolean, '4']>>,
]
// @ts-expect-error
type error = Concat<null, undefined>