crab

Description:

crab

🦀crab🦀 #

Provides Rust-like Result and Option types, making it easier to handle error and option values.
Defined types #
Result #
Result is the type used for returning and propagating errors.
A simple function returning Result might be defined and used like so:
enum Version { version1, version2 }

Result<Version, String> parseVersion(int versionNum) {
if (versionNum == 1) {
return const Ok(Version.version1);
}
if (versionNum == 2) {
return const Ok(Version.version2);
}
return const Err('invalid version');
}

void main() {
final version = parseVersion(1);
// Define processing for success and error
if (version.isErr) {
print('error parsing header: ${version.unwrapErr()}');
} else {
print('working with version: ${version.unwrap()}');
}

// It can also be defined as follows
parseVersion(1).mapOrElse(
(err) => print('error parsing header: $err'),
(v) => print('working with version: $v'),
);
}
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Option #
Type Option represents an optional value: every Option is either Some and contains a value, or None, and does not.
Dart already supports null safety by appending a ? to a type, but you can use the Option type to enhance the handling of optional value (which can also be interpreted as nullable values).
A simple function returning Option might be defined and used like so:
Option<int> getVersionNum(List<int> header) {
if (header.isEmpty) {
return const None();
}
return Some(header.first);
}

void main() {
final versionNum = getVersionNum([1, 2, 3, 4]);
// Define the processing when the value can be obtained and when it cannot be
// obtained
if (versionNum.isNone) {
print('invalid header length');
} else {
print('version number: ${versionNum.unwrap()}');
}

// The above process is equivalent to the following process
getVersionNum([1, 2, 3, 4]).mapOrElse(
() => print('invalid header length'),
(vn) => print('version number: $vn'),
);
}
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References #
This package was created with reference to the following implementation and description of Rust.
Result #

Implementation: https://doc.rust-lang.org/stable/std/result/enum.Result.html
Module description: https://doc.rust-lang.org/stable/std/result/index.html

Option #

Implementation: https://doc.rust-lang.org/stable/std/option/enum.Option.html
Module description: https://doc.rust-lang.org/stable/std/option/index.html