Utility method for dealing with SQLites boolean type in a Typescript codebase

sqliteBool.ts

type SqliteBool<T extends number | boolean> = T extends number ? boolean : number

/**
 * Converts an sqlite bool (0 or 1) to a real bool, and vice versa.
 * 
 * @example
 * sqliteBool(1) // => true
 * sqliteBool(true) // => 1
 */
export function sqliteBool<T extends number | boolean>(value: T): SqliteBool<T> {
    // Uses conditional types to flip between the types.
    // - https://www.typescriptlang.org/docs/handbook/2/conditional-types.html
    //
    // Unfortunately the docs conveniently leave out how to implement
    // a function body using this trick, which is ugly as hell, see
    // here:
    // - https://stackoverflow.com/a/67403992

    if (typeof value === "number") {
        if (value === 1) {
            return true as unknown as SqliteBool<T>
        } else if (value === 0) {
            return false as unknown as SqliteBool<T>
        } else {
            throw Error(`Expected 0 or 1, got ${value}`)
        }
    }

    if (typeof value === "boolean") {
        return (value ? 1 : 0) as unknown as SqliteBool<T>
    }

    throw Error(`Expected number or bool, was ${typeof value}`)
}