type Concat<T extends readonly any[], U extends readonly any[]> = [...T, ...U]
Solution by horoshopodumaj #37996
// A helper type representing any readonly tuple or array.
// Used to check whether a value already behaves like a tuple.
type Tuple = readonly unknown[]
// Concat merges two values while keeping tuple semantics intact.
//
// How it behaves:
// 1. tuple + tuple
// → both tuples are spread and merged into one
//
// 2. tuple + non-tuple
// → the value is appended to the end of the tuple
//
// 3. non-tuple + tuple
// → the value is prepended to the beginning of the tuple
//
// 4. non-tuple + non-tuple
// → both values are wrapped into a new tuple
//
// This ensures:
// - order is preserved
// - tuple length is accurate
// - literal types are not widened
type Concat<Left, Right> =
Left extends Tuple
? Right extends Tuple
? [...Left, ...Right]
: [...Left, Right]
: Right extends Tuple
? [Left, ...Right]
: [Left, Right]
// Converts any input into a tuple form.
//
// Behavior:
// - If the input is already a tuple, keep it as-is
// - If the input is a single value, wrap it in a tuple
//
// This gives us a consistent shape to work with
// and avoids branching logic later.
type AsTuple<Value> =
Value extends readonly unknown[] ? Value : [Value]
// Concat works by first normalizing both inputs into tuples
// and then merging them using tuple spread syntax.
//
// Because both sides are guaranteed to be tuples at this point:
// - order is preserved
// - tuple length is computed correctly
// - literal types remain intact
//
// This approach favors composition over conditional branching
// and is easier to read, reuse, and maintain.
type Concat<Left, Right> = [
...AsTuple<Left>,
...AsTuple<Right>
]
Solution by Muntazir-sd #37955
// 解答をここに記入
type Concat<T extends readonly any[], U extends readonly any[]> = [...T,...U]
Solution by tac-tac-go #37903
// your answers
type Concat<T extends any[], U extends any[]> = [...T, ...U];
Solution by istamal #37897
type Concat<T extends readonly unknown[], U extends readonly unknown[]> = [...T, ...U];
Solution by Hansol46 #37836
type Concat<A1 extends readonly any[], A2 extends readonly any[]> = [...A1, ...A2];
Solution by pkutsenko #37828
// your answers
Solution by Brahima-Fofana #37762
type Concat<T, U> = T extends readonly unknown[]
? U extends readonly unknown[]
? [...T, ...U]
: T
: U extends readonly unknown[]
? U
: []
Solution by rauf322 #37704
// your answers
type Concat<T extends readonly unknown[], U extends readonly unknown[]> = [...T, ...U]
Solution by AlexanderNP #37668
type Concat<T extends readonly unknown[], U extends readonly unknown[]> = [...T, ...U]
// your answers
Solution by AndSLASH #37663
type Concat<T extends readonly any[] , U extends readonly any[]> = [...T , ...U]
Solution by BernTheSeal #37657
type Concat<T extends readonly any[], U extends readonly any[]> = [...T, ...U]
Solution by tomo-local #37580
// your answers
type Concat<T, U> = T extends readonly any[] ? U extends readonly any[] ? [...T,...U] : never : error
Solution by PAVANT009 #37567
type Concat<T extends readonly unknown[], U extends readonly unknown[]> = [...T, ...U]
<T extends readonly unknown[], U extends readonly unknown[]>
T must be a readonly array (tuple) of any types.U must also be a readonly array (tuple) of any types.readonly ensures it works with literal tuples like ["a", "b"] as const.[...T, ...U]
This is a tuple spread type.
It creates a new tuple type by taking:
T, followed byU.The result is a tuple that represents concatenation at the type level.
Concat<T, U> constructs a new tuple type by:
T.U.✅ Example:
type A = [1, 2]
type B = ["a", "b"]
type Result = Concat<A, B>
// Result: [1, 2, "a", "b"]
So Result is exactly [1, 2, "a", "b"]. 🎯
Solution by 3aluw #37460
type Concat<T extends readonly any[], U extends readonly any[]> = [...T, ...U];
Solution by Nakamura25257 #37261
type Tuple = readonly unknown[];
type Concat<T extends Tuple, U extends Tuple> = [...T, ...U];
Solution by djdidi #37133
type Concat<T extends readonly any[], U extends readonly any[]> = [...T, ...U]
Solution by 359Steve #37018
type Tuple= readonly unknown[]
type Concat<T extends Tuple, U extends Tuple> = [...T,...U]
Solution by Anonymous961 #36973
// 你的答案
type Concat<T extends readonly any[], U extends readonly any[]> = [...T, ...U];
Solution by 180ParkerLi #36923
// your answers
type Concat<T extends readonly any[], U extends readonly any[]> = [...T, ...U];
Solution by AlexBraunMagic #36914
type Concat<T extends readonly unknown[], U extends readonly unknown[]> = [...T, ...U];
Solution by shaishab316 #36846
type Result = Concat<[1], [2]> // expected to be [1, 2]
// 你的答案
type Concat<T extends readonly any[], U extends readonly any[]> = [...T,...U]
Solution by mola-fish #36833
type Concat<T extends any[], U extends any[]> = [...T, ...U];
/* _____________ Test Cases _____________ */
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>
Solution by AnastasiaSv #36766
type Concat<T extends readonly unknown[], U extends readonly unknown[]> = [...T, ...U]
Solution by Abdullah-Elsayed01 #36752
type Concat<T extends readonly any[], U extends readonly any[]> = [...T, ...U]
Solution by tungulin #36717
type Concat<T extends T[], U extends U[]> = [...T, ...U]
Solution by Mamdouhreda #36709
// 여기 풀이를 입력하세요
type Concat<T extends unknown[], U extends unknown[]> = [...T, ...U]
Solution by seungdeok #36667
type Tuple = typeof tuple | any[]
type Concat<T extends Tuple, U extends Tuple> = [...T, ...U]
Solution by wiJeeXu #36650
// 你的答案
type Concat<T extends any[] | readonly any[], U extends any[] | readonly any[]> = [...T, ...U]
Solution by MrSissel #36585
type Concat<T extends any[], U extends any[]> = [...T, ...U]
Solution by ChemieAi #36554