Function mapOrElse

Map over a Result instance as in map and get out the value if result is Ok, or apply a function (orElseFn) to the value wrapped in the Err to get a default value.

Like mapOr but using a function to transform the error into a usable value instead of simply using a default value.

Examples

import { ok, err, mapOrElse } from 'true-myth/result';

const summarize = (s: string) => `The response was: '${s}'`;
const getReason = (err: { code: number, reason: string }) => err.reason;

const okResponse = ok("Things are grand here.");
const mappedOkAndUnwrapped = mapOrElse(getReason, summarize, okResponse);
console.log(mappedOkAndUnwrapped);  // The response was: 'Things are grand here.'

const errResponse = err({ code: 500, reason: 'Nothing at this endpoint!' });
const mappedErrAndUnwrapped = mapOrElse(getReason, summarize, errResponse);
console.log(mappedErrAndUnwrapped);  // Nothing at this endpoint!
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Typeparam

T The type of the wrapped Ok value.

Typeparam

U The type of the resulting value from applying mapFn to the Ok value or orElseFn to the Err value.

Typeparam

E The type of the wrapped Err value.