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Refer: Medium - Last of Array
Describe
Implement a generic Last<T>
that takes an Array T and returns its last element.
For example
code snippetCopytypescripttype arr1 = ['a', 'b', 'c']
type arr2 = [3, 2, 1]
type tail1 = Last<arr1> // expected to be 'c'
type tail2 = Last<arr2> // expected to be 1
Test Cases
code snippetCopytypescriptimport { Equal, Expect } from '@type-challenges/utils'
type cases = [Expect<Equal<Last<[3, 2, 1]>, 1>>, Expect<Equal<Last<[() => 123, { a: string }]>, { a: string }>>]
Solution
code snippetCopytypescript// my solution (It may be a little complicated 🤣)
type Last<T extends any[]> = T extends [infer P, ...infer K]
? K['length'] extends 1
? K[0]
: K['length'] extends 0
? P
: Last<K>
: never
// other solution (In js, rest element must be last element!)
type Last<T extends any[]> = T extends [...infer _, infer Z] ? Z : never