Implement a type LengthOfString<S> just like Array#length:
Differing to two previous challenges about strings' length, this times the type must support strings about $10^6$ characters long, which makes it more challenging.
import type { Equal, Expect } from '@type-challenges/utils'
type Deced = [10, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
type Signum = Deced[number]
type Reped<
S extends string,
C extends Signum,
R extends string = '',
>
= (C extends 0
? R
: Reped<S, Deced[C], `${R}${S}`>
)
type t0 = 'k'
type t1 = Reped<t0, 10>
type t2 = Reped<t1, 10>
type t3 = Reped<t2, 10>
type t4 = Reped<t3, 10>
type t5 = Reped<t4, 10>
type t6 = Reped<t5, 10>
type Signums<
N extends string,
Acc extends readonly Signum[] = [],
> = N extends `${infer Head extends Signum}${infer Rest}`
? Signums<Rest, [...Acc, Head]>
: Acc
type Gened<N extends string> = Signums<N> extends [
infer N6 extends Signum,
infer N5 extends Signum,
infer N4 extends Signum,
infer N3 extends Signum,
infer N2 extends Signum,
infer N1 extends Signum,
infer N0 extends Signum,
] ? `${''
}${Reped<t6, N6>
}${Reped<t5, N5>
}${Reped<t4, N4>
}${Reped<t3, N3>
}${Reped<t2, N2>
}${Reped<t1, N1>
}${Reped<t0, N0>
}` : never
type cases = [
Expect<Equal<LengthOfString<Gened<'0000000'>>, 0>>,
Expect<Equal<LengthOfString<Gened<'0000001'>>, 1>>,
Expect<Equal<LengthOfString<Gened<'0000002'>>, 2>>,
Expect<Equal<LengthOfString<Gened<'0000003'>>, 3>>,
Expect<Equal<LengthOfString<Gened<'0000004'>>, 4>>,
Expect<Equal<LengthOfString<Gened<'0000005'>>, 5>>,
Expect<Equal<LengthOfString<Gened<'0000055'>>, 55>>,
Expect<Equal<LengthOfString<Gened<'0000555'>>, 555>>,
Expect<Equal<LengthOfString<Gened<'0005555'>>, 5555>>,
Expect<Equal<LengthOfString<Gened<'0055555'>>, 55555>>,
Expect<Equal<LengthOfString<Gened<'8464592'>>, 8464592>>,
Expect<Equal<LengthOfString<Gened<'1373690'>>, 1373690>>,
Expect<Equal<LengthOfString<Gened<'1707793'>>, 1707793>>,
Expect<Equal<LengthOfString<Gened<'0196268'>>, 196268>>,
Expect<Equal<LengthOfString<Gened<'6646734'>>, 6646734>>,
Expect<Equal<LengthOfString<Gened<'0538159'>>, 538159>>,
Expect<Equal<LengthOfString<Gened<'0058901'>>, 58901>>,
Expect<Equal<LengthOfString<Gened<'8414001'>>, 8414001>>,
Expect<Equal<LengthOfString<Gened<'1740697'>>, 1740697>>,
Expect<Equal<LengthOfString<Gened<'2281441'>>, 2281441>>,
]