typescript fun with generics

ts-fun.ts

// Was having some fun with TypeScript and built a signature for some theoretical
// object that could cast any type to any other type. This uses template literal types,
// generics, infer and mapped types.

import {Except} from 'type-fest';

type TypeofsTypes = {
	string: string;
	number: number;
	bigint: BigInt;
	boolean: boolean;
	symbol: symbol;
	undefined: undefined;
	object: Record<string | number | symbol, unknown>;
	function: (...args: unknown[]) => unknown;
};

type Typeofs = keyof TypeofsTypes;

type ToTypeofs<T> = Except<TypeofsTypes, 'object'> & {
	object: {value: T};
};

type TO = 'to';
type SubtractTo<T extends string> = T extends `${TO}${infer X}` ? Uncapitalize<X> : never;
type AddTo<T extends string> = `${TO}${Capitalize<T>}`;

declare const handlers: {
	[FromType in Typeofs]: {
		[ToType in AddTo<Typeofs>]: (
			from: TypeofsTypes[FromType]
		) => ToTypeofs<TypeofsTypes[FromType]>[SubtractTo<ToType>];
	};
};

handlers.string.toObject('hello');