Refer: Easy - Push

Describe

Implement the generic version of Array.push

For example

code snippetCopytypescript
type Result = Push<[1, 2], '3'> // [1, 2, '3']

Test Cases

code snippetCopytypescript
import { Equal, Expect, ExpectFalse, NotEqual } from '@type-challenges/utils'

type cases = [
  Expect<Equal<Push<[], 1>, [1]>>,
  Expect<Equal<Push<[1, 2], '3'>, [1, 2, '3']>>,
  Expect<Equal<Push<['1', 2, '3'], boolean>, ['1', 2, '3', boolean]>>,
  Expect<Equal<Push<['1', 2, '3'], '3'>, ['1', 2, '3']>>,
]

Solution

Question: Push<['1', 2, '3'], '3'> why not equal to ['1', 2, '3', '3'] in Push operation?

It fixed in #7947.

code snippetCopytypescript
// my solution
type Push<T extends any[], U> = T['length'] extends 0
  ? [U]
  : T extends [...infer P, infer K]
  ? K extends U
    ? T
    : [...T, U]
  : never

// other solutions
type Push<T extends any[], U> = [U] extends [T[number]] ? T : [...T, U]

The reason of wrapped U and T[number] is refer to here.