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Refer: Medium - Flatten
Describe
In this challenge, you would need to write a type that takes an array and emitted the flatten array type.
For example:
code snippetCopytypescripttype flatten = Flatten<[1, 2, [3, 4], [[[5]]]]> // [1, 2, 3, 4, 5]
Test Cases
code snippetCopytypescriptimport { Equal, Expect } from '@type-challenges/utils'
type cases = [
Expect<Equal<Flatten<[]>, []>>,
Expect<Equal<Flatten<[1, 2, 3, 4]>, [1, 2, 3, 4]>>,
Expect<Equal<Flatten<[1, [2]]>, [1, 2]>>,
Expect<Equal<Flatten<[1, 2, [3, 4], [[[5]]]]>, [1, 2, 3, 4, 5]>>,
Expect<Equal<Flatten<[{ foo: 'bar'; 2: 10 }, 'foobar']>, [{ foo: 'bar'; 2: 10 }, 'foobar']>>,
]
Solution
code snippetCopytypescripttype Flatten<T extends any[], C extends any[] = []> = T extends [infer P, ...infer K]
? P extends any[]
? Flatten<[...P, ...K], C>
: Flatten<K, [...C, P]>
: C