AI solution for TypeScript puzzle on BFE.dev
35. implement Filter<T, A>

type Filter<T extends any[], A> = {
  [K in keyof T]: T[K] extends A ? T[K] : never;
}[number];

Explanation:

• We start by defining a generic array type T and a generic type A.
• We use the keyof keyword to get the union of all the keys in the array.
• We iterate over each key K in the union of keys using the in keyword.
• For each key K, we check if the corresponding element in T extends the type A. If it does, we return the element, otherwise we return never.
• Finally, we use the number index type to get a tuple type of only the elements that extend A.

Note:

• The Filter type only returns the first occurrence of each element that extends A. If there are multiple occurrences, they will be removed.
• The Filter type does not preserve the order of elements in the original array.