result.ts

/**
 * @summary The Result<Ok, Error> interface describes the result of a function that can occur in two different ways, being an error or a positive result.
 * @summary The methods in this interface help the developer to better understand the result of the function and then deal with it directly.
 * @summary Use ``Ok(value)`` or ``Err(error)`` to instantiate this.
 */
export interface Result<Ok = any, Err = Error> {
    isOk(): boolean,
    isErr(): boolean,
    /**
     * @throws "Tried to unwrap an error value but the value is ok." - When you try to unwrap an ok value as error.
     */
    unwrapErr(): Err,
    /**
     * @throws "Tried to unwrap an ok value but the value is an error." - When you try to unwrap an error value as ok.
     */
    unwrapOk(): Ok,
    unwrap(): Ok | Err,
    unwrapOrDefault<T>(defaultValue: T): Ok | T
}

export function Ok<T = any, E = Error>(value: T): Result<T, E> {
    return createResult<T, E>({
        isOk: true,
        value
    });
}

export function Err<T = any, E = Error>(value: E): Result<T, E> {
    return createResult<T, E>({
        isOk: false,
        value
    });
}

type ResultOptions<T, E> = {
    isOk: true,
    value: T
} | {
    isOk: false,
    value: E
};

function createResult<T, E>(options: ResultOptions<T, E>): Result<T, E> {
    return Object.freeze({
        isOk() {
            return options.isOk;
        },
        isErr() {
            return !options.isOk;
        },
        unwrapErr() {
            if (!options.isOk)
                return options.value;

            throw `Tried to unwrap an error value but the value is ok.`;
        },
        unwrapOk() {
            if (options.isOk)
                return options.value;

            throw `Tried to unwrap an ok value but the value is an error.`;
        },
        unwrap() {
            return options.value;
        },
        unwrapOrDefault<T>(defaultValue: T) {
            return options.isOk ? options.value : defaultValue;
        }
    });
}