@rslike/std
v3.0.1
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JavaScript Standard library without udndefined behavior!
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Rust-Like Standard Library
Make Javascript without undefined behavior. Forgot about try/catch/finally
which breakes your code!
Reasons to install @rsLike/std?
- Less undefined behavior, when using Option and Result.
- Well tested.
100% test coverage
- JSDoc with examples.
- Typescript ready - d.ts types are generated with tsc.
- first-class
CJS
andESM
support. - Zero dependencies.
2kB
for min+gzip and7.6kB
for minified. See in bundlefobia.- Deno?
Installation
NPM:
npm i @rslike/std
YARN/PNPM:
yarn add @rslike/std
pnpm add @rslike/std
Wiki
Avaliable by link: https://github.com/vitalics/rslike/wiki
Adding global functions and classes
- Install package
- In your entry file write next:
// your main file
// add global types in globalThis Some,None,Option, Result,Ok,Err functions
import "@rslike/std/globals";
// rest your file
Related packages
API
Match
Matches the Option
or Result
and calls callback functions.
1 callback function will be executed for Ok
or Some
result.
2 callback function will be executed for Err
or None
result.
If incoming arguments is not Option
or Result
or callback functions is not a functions then it throws an UndefinedBehavior
error.
If your result have type Result<Option<T>, E>
. You need to call match function only once
const resFromBackend = Bind(async (...args) => return (await fetch(...args)).json())
const json = match(await resFromBackend('https://json-placeholder.typicode.com/posts/1'), (res) => {
console.log('JSON is:', unwrapped)
}, (e) => {
if(e){
console.log('Error:', e)
}
else {
console.log('JSON is None(null or undefined)')
}
})
console.log(json); // YOUR JSON from Backend
Bind
Function decorator. Combines Result and Option modules. Make the function safe to execute.
Wraps function and return new function with binded context.
Result of this function will be mapped into Result<Option<T>,E>
.
Function result
will be mapped into Ok(Some(result))
.
undefined
function result will mapped into Ok(None())
.
const fn = (a: number) => a + 2;
const newFn = Bind(fn);
const res = newFn(1);
res.unwrap().unwrap(); // 3
newFn(10).unwrap().unwrap(); // 12
const thrower = () => {
throw new Error("shit happens :)");
};
const func = Bind(thrower);
func().isErr(); // true
const err = func().unwrapErr();
console.log(err); // {message: 'shit happens :)'}
err instanceof Error; // true
// async example
const asyncFn = () => Promise.resolve(123);
const fn = Bind(asyncFn);
const r = await fn();
r.isOk(); // true
r.unwrap(); // 123
Option
Type Option
represents an optional value: every Option
is either Some
and contains a value, or None
, and does not. Option
have a number of uses:
- Initial values
- Return values for functions that are not defined over their entire input range (partial functions)
- Return value for otherwise reporting simple errors, where
None
is returned on error Optional
struct fieldsOptional
function arguments- Nullish(null or undefined) value.
- Swapping things out of difficult situations
- Options are commonly paired with pattern matching to query the presence of a value and take action, always accounting for the
None
case.
Functions
Some(T)
represents Some value
None
Represents nullish(null
or undefiend
) value
Symbols
Symbol.toPrimitive
since 3.x.x
Returns value
from Option
Symbol.toStringTag
since 3.x.x
Symbol.asyncIterator
since 3.x.x
See MDN docs for more
Note: This method will only yeild if the Option
is Some
Note: throws UndefinedBehaviorError
for Some(value)
if value
is not implements Symbol.asyncIterator
Symbol.iterator
since 3.x.x
See MDN docs for more
Note: This method will only yeild if the Option
is Some
Note: throws UndefinedBehaviorError
for Some(value)
if value
is not implements Symbol.iterator
Example:
const a = Some([1, 2, 3]);
for (const el of a) {
console.log("element is:", el);
}
// will prints
// element is: 1
// element is: 2
// element is: 3
const b = Some(1);
// will throws, Symbol.iterator is not suported for number
for (const el of b) {
console.log("element is:", el);
}
const c = Some({
[Symbol.iterator]() {
return 1;
},
});
for (const el of c) {
console.log("iterable:", el);
}
// will prints
// iterable: 1
Symbol.split
implemented since 3.x.x version
See MDN docs for more
NOTE: throws UndefinedBehaviorError
if wrapped value is not a string
or RegExp
example:
const a = Some("bar");
"foobar".split(a); // ["foo", ""]
Symbol.search
implemented since 3.x.x version
See MDN docs for more
NOTE: throws UndefinedBehaviorError
if wrapped value is not a string
or RegExp
Symbol.inspect
util.inspect
is a server feature
The util.inspect()
method returns a string representation of object that is intended for debugging.
See more about Symbol.inspect
Example:
import util from "node:util";
const a = Some(4);
util.inspect(a); // Some(4)
Methods
expect
Returns the contained Some
value, consuming the self value.
const x = Some("value");
x.expect("fruits are healthy") === "value"; // true
const y: Option<string> = None();
y.expect("fruits are healthy"); // throws with `fruits are healthy`
unwrap
Returns the contained Some
value, consuming the self value.
Because this function may throws, its use is generally discouraged. Instead, prefer to use pattern matching and handle the None case explicitly, or call unwrapOr
, unwrapOrElse
, or unwrapOrDefault
.
Throws an error when value is None
const x = Some("air");
x.unwrap() === "air";
const x: Option<string> = None();
x.unwrap(); // fails
unwrapOr
Returns the contained Some
value or a provided default.
const x = Some("air");
x.unwrapOr("another") === "air";
const x: Option<string> = None();
x.unwrapOr("another") === "another";
unwrapOrElse
Returns the contained Some value or computes it from a closure.
const k = 10;
Some(4).unwrapOrElse(() => 2 * k) === 4;
None().unwrapOrElse(() => 2 * k) === 20;
map
Maps an Option<T>
to Option<U>
by applying a function to a contained value (if Some
) or returns None (if None
).
const maybeSomeString = Some("Hello, World!");
const maybeSomeLen = maybeSomeString.map(s => s.length);
maybeSomeLen === Some(13));
const x: Option<string> = None();
x.map(s => s.length) === None();
mapOr
Returns the provided default result (if none
), or applies a function to the contained value (if any).
Arguments passed to mapOr are eagerly evaluated; if you are passing the result of a function call, it is recommended to use mapOrElse
, which is lazily evaluated.
const x = Some("foo");
x.mapOr(42, (v) => v.length) === 3;
const x: Option<string> = None();
x.mapOr(42, (v) => v.len()) === 42;
mapOrElse
Computes a default function result (if none
), or applies a different function to the contained value (if any).
const k = 21;
const x = Some("foo");
x.mapOrElse(
() => 2 * k,
(v) => v.length,
) === 3;
const x: Option<string> = None();
x.mapOrElse(
() => 2 * k,
(v) => v.length,
) === 42;
okOr
Transforms the Option<T>
into a Result<T, E>
, mapping Some(v)
to Ok(v)
and None
to Err(err)
.
Arguments passed to okOr
are eagerly evaluated; if you are passing the result of a function call, it is recommended to use okOrElse
, which is lazily evaluated.
const x = Some("foo");
String(x.okOr(0)) === String(Ok("foo"));
const y: Option<string> = None();
y.okOr(0) === Err(0);
okOrElse
Transforms the Option<T>
into a Result<T, E>
, mapping Some(v)
to Ok(v)
and None to Err(err())
.
const x = Some("foo");
console.assert(x.okOrElse(() => 0) === Ok("foo"));
let y: Option<string> = None();
console.assert(y.okOrElse(() => 0) === Err(0));
and
Returns None
if the option is None
, otherwise returns optb
.
Arguments passed to and are eagerly evaluated; if you are passing the result of a function call, it is recommended to use andThen
, which is lazily evaluated.
const x = Some(2);
const y: Option<string> = None();
console.assert(x.and(y) === None());
// another example
let x: Option<number> = None();
let y = Some("foo");
console.assert(x.and(y) === None());
// another example
let x = Some(2);
let y = Some("foo");
console.assert(x.and(y) === Some("foo"));
// another example
let x: Option<number> = None();
let y: Option<string> = None();
console.assert(x.and(y) === None());
andThen
Returns None
if the option is None
, otherwise calls f with the wrapped value and returns the result.
Some languages call this operation flatmap.
function toString(x: number): Option<string> {
return Some(String(x));
}
console.assert(Some(2).andThen(toString) === Some(2.toString()));
console.assert(None().andThen(toString) === None());
filter
Returns None
if the option is None
, otherwise calls predicate with the wrapped value and returns:
Some(t)
if predicate returns true (where t is the wrapped value), an
None
if predicate returns false
function isEven(n: number): boolean {
return n % 2 == 0;
}
console.assert(None().filter(isEven) === None());
console.assert(Some(3).filter(isEven) === None());
console.assert(Some(4).filter(isEven) === Some(4));
xor
Returns Some
if exactly one of self, optb
is Some
, otherwise returns None
.
insert
Inserts value into the option, then returns a mutable reference to it.
If the option already contains a value, the old value is dropped.
See also getOrInsert
, which doesn’t update the value if the option already contains Some
.
const opt = None();
const val = opt.insert(1);
console.assert(val === 1);
console.assert(opt.unwrap() === 1);
// another example
const val = opt.insert(2);
console.assert(val === 2);
replace
Replaces the actual value in the option by the value given in parameter, returning the old value if present, leaving a Some
in its place without deinitializing either one.
const x = Some(2);
const old = x.replace(5);
console.assert(x === Some(5));
console.assert(old === Some(2));
// another example
const x = None();
const old = x.replace(3);
console.assert(x === Some(3));
console.assert(old === None());
zip
Zips self with another Option
.
If self is Some(s)
and other is Some(o)
, this method returns Some((s, o))
. Otherwise, None
is returned.
const x = Some(1);
const y = Some("hi");
const z = None<number>();
x.zip(y) === Some((1, "hi"));
x.zip(z) === None();
zipWith
Zips self and another Option
with function f
.
If self is Some(s)
and other is Some(o)
, this method returns Some(f(s, o))
. Otherwise, None
is returned.
class Point {
constructor(
readonly x: number,
readonly y: number,
) {}
static create(x: number, y: number) {
return new Point(x, y);
}
}
const x = Some(17.5);
const y = Some(42.7);
x.zipWith(y, Point.create) === Some({ x: 17.5, y: 42.7 });
unzip
Unzips an option containing a tuple of two options.
If self is Some((a, b))
this method returns (Some(a), Some(b))
. Otherwise, (None, None)
is returned.
const x = Some([1, "hi"]);
const y = None<[number, number]>();
console.assert(x.unzip() === [Some(1), Some("hi")]);
console.assert(y.unzip() === [None(), None()]);
flatten
Converts from Option<Option<T>>
to Option<T>
.
const x: Option<Option<number>> = Some(Some(6));
Some(6) === x.flatten();
const x: Option<Option<number>> = Some(None());
None() === x.flatten();
const x: Option<Option<number>> = None();
None() === x.flatten();
isSome
Returns true
if the option is a Some
value.
const x: Option<number> = Some(2);
x.isSome() === true; // true
const x: Option<number> = None();
x.isSome() === false; // true
isNone
Returns true if the option is a None
value.
isSomeAnd
Returns true
if the option is a Some
and the value inside of it matches a predicate.
const x: Option<number> = Some(2);
x.isSomeAnd((x) => x > 1) === true; // true
const x: Option<number> = Some(0);
x.isSomeAnd((x) => x > 1) === false; // true
const x: Option<number> = None();
x.isSomeAnd((x) => x > 1) === false; // true
getOrInsert
Inserts value into the option if it is None
, then returns a mutable reference to the contained value.
See also insert
, which updates the value even if the option already contains Some
.
const x = None<number>();
const y = x.getOrInsert(7);
y === 7; // true
getOrInsertWith
Inserts a value computed from f
into the option if it is None
, then returns the contained value.
const x = None<number>();
const y = x.getOrInsertWith(() => 5);
y === 5; // true
or
Returns the Option
if it contains a value, otherwise returns optb
. Arguments passed to or are eagerly evaluated; if you are passing the result of a function call, it is recommended to use orElse
, which is lazily evaluated.
const x = Some(2);
const y = None();
console.assert(x.or(y) === Some(2));
// another example
const x = None();
const y = Some(100);
console.assert(x.or(y) === Some(100));
// another example
let x = Some(2);
let y = Some(100);
console.assert(x.or(y) === Some(2));
// another example
const x: Option<number> = None();
const y = None();
console.assert(x.or(y) === None());
orElse
Returns the Option
if it contains a value, otherwise calls f
and returns the result.
function nobody(): Option<string> {
return None();
}
function vikings(): Option<string> {
return Some("vikings");
}
Some("barbarians").orElse(vikings) === Some("barbarians"); // true
None().orElse(vikings) === Some("vikings"); // true
None().orElse(nobody) === None(); // true
Boolean Operators
These methods treat the Option
as a boolean value, where Some
acts like true and None
acts like false. There are two categories of these methods: ones that take an Option
as input, and ones that take a function as input (to be lazily evaluated).
The and
, or
, and xor
methods take another Option as input, and produce an Option
as output. Only the and method can produce an Option<U>
value having a different inner type U than Option<T>
.
| method | self | input | output | | ------ | ------- | --------- | ------- | | and | None | (ignored) | None | | and | Some(x) | None | None | | and | Some(x) | Some(y) | Some(y) | | or | None | None | None | | or | None | Some(y) | Some(y) | | or | Some(x) | (ignored) | Some(x) | | xor | None | None | None | | xor | None | Some(y) | Some(y) | | xor | Some | None | Some(x) | | xor | Some(x) | Some(y) | None |
The andThen
and orElse
methods take a function as input, and only evaluate the function when they need to produce a new value. Only the andThen
method can produce an Option<U>
value having a different inner type U
than Option<T>
.
| method | self | function input | function result | output |
| --------- | ------- | -------------- | --------------- | ------- |
| andThen
| None | (not provided) | (not evaluated) | None |
| andThen
| Some(x) | x | None | None |
| andThen
| Some(x) | x | Some(y) | Some(y) |
| orElse
| None | (not provided) | None | None |
| orElse
| None | (not provided) | Some(y) | Some(y) |
| orElse
| Some(x) | (not provided) | (not evaluated) | Some(x) |
This is an example of using methods like andThen
and or in a pipeline of method calls. Early stages of the pipeline pass failure values (None
) through unchanged, and continue processing on success values (Some
). Toward the end, or substitutes an error message if it receives None.
Result
Result<T, E>
is the type used for returning and propagating errors. It is an enum with the variants, Ok(T)
, representing success and containing a value, and Err(E)
, representing error and containing an error value.
Functions
Ok(T)
Represents success with T
value.
Err(E)
Represents fail with some error inside.
Symbols
Symbol.toPrimitive
Symbol.toStringTag
Symbol.iterator
See MDN docs for more
Note: This method will only yeild if the Option
is Some
Note: throws UndefinedBehaviorError
for Ok(value)
if value
is not implements Symbol.iterator
Err
value is not iterable.
Example:
const a = Ok([1, 2, 3]);
for (const el of a) {
console.log("element is:", el);
}
// will prints
// element is: 1
// element is: 2
// element is: 3
const b = Ok(1);
// will throws, Symbol.iterator is not suported for number
for (const el of b) {
console.log("element is:", el);
}
const c = Ok({
[Symbol.iterator]() {
return 1;
},
});
for (const el of c) {
console.log("iterable:", el);
}
// will prints
// iterable: 1
Symbol.asyncIterator
since 3.x.x
See MDN docs for more
Note: This method will only yeild if the Option
is Some
Note: throws UndefinedBehaviorError
for Some(value)
if value
is not implements Symbol.asyncIterator
Symbol.split
Symbol.search
Symbol.inspect
Symbol.inspect
util.inspect
is a server feature
The util.inspect()
method returns a string representation of object that is intended for debugging.
See more about Symbol.inspect
Example:
import util from "node:util";
const a = Ok(4);
util.inspect(a); // Ok(4)
util.inspect(Err("some error")); // Err('some error')
Methods
expect
Returns the contained Ok
value, consuming the self value.
Because this function may throws, its use is generally discouraged. Call unwrapOr
, unwrapOrElse
.
Panics if the value is an Err
, with a message including the passed message, and the content of the Err
.
const x: Result<number, string> = Err("emergency failure");
x.expect("Testing expect"); // `Testing expect`, cause: emergency failure
unwrap
Returns the contained Ok
value, consuming the self value.
Because this function may throws, its use is generally discouraged. Instead, call unwrapOr
, unwrapOrElse
.
const x: Result<number, string> = Ok(2);
x.unwrap() === 2;
unwrapOr
eturns the contained Ok
value or a provided default.
Arguments passed to unwrapOr
are eagerly evaluated; if you are passing the result of a function call, it is recommended to use unwrapOrElse
, which is lazily evaluated.
const fallback = 2;
const x = Ok(9);
x.unwrapOr(fallback) === 9; // true
cosnt x: Result<number, string> = Err("error");
x.unwrapOr(fallback) === fallback; // true
isOk
Returns true
if the result is Ok
.
const x: Result<number, string> = Ok(-3);
x.isOk(); // true
// another example
let x: Result<number, string> = Err("Some error message");
x.isOk(); // false
isOkAnd
Returns true
if the result is Ok
and the value inside of it matches a predicate.
const x: Result<number, string> = Ok(2);
console.assert(x.isOkAnd((x) => x > 1) === true);
// another example
const x: Result<number, string> = Ok(0);
console.assert(x.isOkAnd((x) => x > 1) === false);
// another example
const x: Result<number, string> = Err("hey");
console.assert(x.isOkAnd((x) => x > 1) === false);
isErr
Returns true
if the result is Err
.
const x: Result<number, string> = Ok(-3);
console.assert(x.isErr() === false);
// another example
const x: Result<number, string> = Err("Some error message");
console.assert(x.isErr() === true);
isErrAnd
Returns true
if the result is Err
and the value inside of it matches a predicate.
const x: Result<number, Error> = Err(new Error("not found"));
x.isErrAnd((e) => e.message === "not found"); // true;
// another example
const x: Result<number, Error> = Err(new Error("permission denied"));
x.isErrAnd((x) => x.name === "TypeError"); // false
// another example
const x: Result<number, Error> = Ok(123);
x.isErrAnd((e) => e.name == "Error"); // false
ok
Converts self into an Option<T>
, consuming self, and discarding the error, if any.
const x: Result<number, string> = Ok(2);
x.ok() === Some(2); // true
// another example
const x: Result<number, string> = Err("Nothing here");
x.ok() === None(); // true
err
Converts self into an Option<E>
, consuming self, and discarding the success value, if any.
const x: Result<number, string> = Ok(2);
x.err() === None(); // true
const x: Result<number, string> = Err("Nothing here");
x.err() === Some("Nothing here"); // true
map
Maps a Result<T, E>
to Result<U, E>
by applying a function to a contained Ok value, leaving an Err
value untouched.
This function can be used to compose the results of two functions.
const x = Ok(1);
x.map((v) => v * 2) === Ok(2); // true
mapOr
Returns the provided default (if Err
), or applies a function to the contained value (if Ok
),
Arguments passed to mapOr
are eagerly evaluated; if you are passing the result of a function call, it is recommended to use mapOrElse
, which is lazily evaluated.
const x: Result<string, string> = Ok("foo");
x.mapOr(42, (v) => v.length); // result is 3
// another example
const x: Result<number, string> = Err("bar");
x.mapOr(42, (v) => v.length); // 42
mapOrElse
Maps a Result<T, E>
to U
by applying fallback function default to a contained Err
value, or function f
to a contained Ok
value.
This function can be used to unpack a successful result while handling an error.
let k = 21;
const x: Result<string, string> = Ok("foo");
x.mapOrElse(
(err) => k * 2,
(v) => v.length,
); // 3
const y: Result<string, string> = Err("bar");
y.mapOrElse(
(e) => k * 2,
(v) => v.length,
); // 42
mapErr
Maps a Result<T, E>
to Result<T, F>
by applying a function to a contained Err value, leaving an Ok
value untouched.
This function can be used to pass through a successful result while handling an error.
const stringify = (x: number) => `error code: ${x}`;
const x: Result<number, number> = Ok(2);
x.mapErr(stringify) === Ok(2); // true
const y: Result<number, number> = Err(13);
y.mapErr(stringify) === Err("error code: 13");
expectErr
Returns the contained Err
value, consuming the self value.
const x: Result<number, string> = Ok(10);
x.expectErr("Testing expectErr"); // throws `Testing expectErr; cause: 10`
unwrapErr
Returns the contained Err
value, consuming the self value.
const x: Result<number, string> = Err("emergency failure");
x.unwrapErr() === "emergency failure";
unwrapOrElse
Returns the contained Ok
value or computes it from a closure.
const count = (x: string) => x.length;
Ok(2).unwrapOrElse(count) === 2; // true
Err("foo").unwrapOrElse(count) === 3; // true
and
Returns res if the result is Ok, otherwise returns the Err value of self.
Arguments passed to and are eagerly evaluated; if you are passing the result of a function call, it is recommended to use andThen, which is lazily evaluated.
const x: Result<number, string> = Ok(2);
const y: Result<string, string> = Err("late error");
x.and(y) === Err("late error"); // true
// another example
const x: Result<number, string> = Err("early error");
const y: Result<string, string> = Ok("foo");
x.and(y) === Err("early error"); // true
// another example
const x: Result<number, string> = Err("not a 2");
const y: Result<string, string> = Err("late error");
x.and(y) === Err("not a 2"); // true
// another example
const x: Result<number, string> = Ok(2);
const y: Result<string, string> = Ok("different result type");
x.and(y) === Ok("different result type"); // true
andThen
Calls op if the result is Ok
, otherwise returns the Err
value of self.
This function can be used for control flow based on Result
values.
const sqThenToString = (x: number) => {
return Ok(x * x).map(sq => sq.toString())
}
Ok(2).andThen(sqThenToString) === Ok(4.toString())); // true
Err("not a number").andThen(sqThenToString) === Err("not a number"); // true
or
Returns res if the result is Err, otherwise returns the Ok value of self.
Arguments passed to or are eagerly evaluated; if you are passing the result of a function call, it is recommended to use orElse, which is lazily evaluated.
const x: Result<number, string> = Ok(2);
const y: Result<number, string> = Err("late error");
x.or(y) === Ok(2); // true
// another example
const x: Result<number, string> = Err("early error");
const y: Result<number, string> = Ok(2);
x.or(y) === Ok(2); // true
// another example
const x: Result<number, string> = Err("not a 2");
const y: Result<number, string> = Err("late error");
x.or(y) === Err("late error"); // true
// another example
const x: Result<number, string> = Ok(2);
const y: Result<number, string> = Ok(100);
x.or(y) === Ok(2); // true
orElse
Calls fn if the result is Err
, otherwise returns the Ok
value of self.
This function can be used for control flow based on result values.
const sq = (x: number) => Ok(x * x);
const err = (x: number) => Err(x);
Ok(2).orElse(sq).orElse(sq) === Ok(2); // true
Ok(2).orElse(err).orElse(sq) === Ok(2); // true
Err(3).orElse(sq).orElse(err) === Ok(9); // true
Err(3).orElse(err).orElse(err) === Err(3); // true
flatten
Converts from Result<Result<T, E>, E>
to Result<T, E>
const x: Result<Result<string, number>, number> = Ok(Ok("hello"));
Ok("hello") === x.flatten(); // true
const x: Result<Result<string, number>, number> = Ok(Err(6));
Err(6) === x.flatten(); // true
const x: Result<Result<string, number>, number> = Err(6);
Err(6) === x.flatten(); // true
Boolean Operators
These methods treat the Result
as a boolean value, where Ok
acts like true and Err
acts like false. There are two categories of these methods: ones that take a Result
as input, and ones that take a function as input (to be lazily evaluated).
The and and or methods take another Result
as input, and produce a Result
as output. The and method can produce a Result<U, E>
value having a different inner type U
than Result<T, E>
. The or method can produce a Result<T, F>
value having a different error type F
than Result<T, E>
.
| method | self | input | output |
| ------ | ------ | --------- | ------ |
| and
| Err(e) | (ignored) | Err(e) |
| and
| Ok(x) | Err(d) | Err(d) |
| and
| Ok(x) | Ok(y) | Ok(y) |
| or
| Err(e) | Err(d) | Err(d) |
| or
| Err(e) | Ok(y) | Ok(y) |
| or
| Ok(x) | (ignored) | Ok(x) |
The andThen
and orElse
methods take a function as input, and only evaluate the function when they need to produce a new value. The andThen
method can produce a Result<U, E>
value having a different inner type U
than Result<T, E>
. The orElse
method can produce a Result<T, F>
value having a different error type F
than Result<T, E>
.
| method | self | function input | function result | output |
| --------- | ------ | -------------- | --------------- | ------ |
| andThen
| Err(e) | (not provided) | (not evaluated) | Err(e) |
| andThen
| Ok(x) | x | Err(d) | Err(d) |
| andThen
| Ok(x) | x | Ok(y) | Ok(y) |
| orElse
| Err(e) | e | Err(d) | Err(d) |
| orElse
| Err(e) | e | Ok(y) | Ok(y) |
| orElse
| Ok(x) | (not provided) | (not evaluated) | Ok(x) |