Some useful type manipulations

types.ts

// why [A]? check https://github.com/microsoft/TypeScript/issues/31751
type Equal<A, B> = 
  [A] extends [B] ?
    [B] extends [A] ?
      true :
    false :
  false

// [A, ...?] -> A
type First<T> =
  T extends [infer R, ...unknown[]] ?
    R :
  T extends (infer R)[] ?
    R :
  never

// [?, ...A] -> A
type Rest<T> =
  T extends [unknown, ...infer Rest] ?
    Rest :
  T extends [] ?
    never :
  T extends (infer R)[] ?
    T :
  never

There is also nice type manipulation library - utility-types.