AI solution for TypeScript puzzle on BFE.dev
55. implement StringToNumber<S>

type StringToNumber<S extends string> = S extends `${infer First}${infer Rest}`  ? First extends keyof Numbers    ? Numbers[First] extends never      ? never      : Numbers[First] extends number      ? `${Numbers[First]}${StringToNumber<Rest>}`      : never    : never  : 0;type Numbers = {  '0': 0;  '1': 1;  '2': 2;  '3': 3;  '4': 4;  '5': 5;  '6': 6;  '7': 7;  '8': 8;  '9': 9;};

In the above solution, we use conditional types to check whether the first character of the string is a valid digit (0-9). Then, we recursively call the StringToNumber type to convert the rest of the string to a number. If the first character is not a valid digit, then we return never type to indicate a type error.

We also define a Numbers type which associates the digits 0-9 with their respective numeric types. This type is used in validating the first character of the string.