- count<T>(p): (<U>(x) => U extends Opt<T>
    ? 0 | 1
    : number) Parameters
p: ((_) => boolean)
- (_): boolean
 Returns boolean
Returns (<U>(x) => U extends Opt<T>
    ? 0 | 1
    : number)
- <U>(x): U extends Opt<T>
    ? 0 | 1
    : number Type Parameters
U extends Opt<T> | readonly T[]
Returns U extends Opt<T>
    ? 0 | 1
    : number
Same as Opt.count, but also supports arrays.