Conveniently.

Write Dart code more conveniently.

This is a tiny package that offers some very convenient utilities that you may use quite often once you know they exist.

Types

Result<V>

The Result type is used to represent the result of a computation. It may be either successful (an instance of Ok) or a failure (of type Fail).

It helps enforce error checking as the caller of a function returning Result is forced to inspect the returned value for errors, as opposed to with Exceptions.

You normally obtain a Result by calling catching or catching$ (see more examples at the end of this page).

final result = catching$(() {
  // run computation that may throw
});

// pattern match to handle the result
Object value = switch (result) {
  Ok(value: var v) => v,
  Fail() => 'error'
};

You can also create a Result by invoking its factory methods:

Result<String> result;
result = Result.ok('yes');
result = Result.fail(FormatException());

To change the type V of a Result<V>, use its map or flatMap functions.

If the mapper function throws, map and flatMap return a Fail Result with a MappingFailureException within it.

Example:

Result<int> result = Result.ok('yes').map((s) => s.length);

Top-level functions

A few functions have both synchronous and async versions. In such cases, the synchronous function's name appends $ to the async function's name. The Dart stdlib normally adds the Sync suffix in such cases, but I thought $ would be a better suffix as it's shorter and I can quickly internalize it as meaning Sync in my head.

• timing - time a computation (asynchronous).
• timing$ - time a computation (synchronous).
• catching - enforce error handling (asynchronous).
• catching$ - enforce error handling (synchronous).
• alwaysTrue - predicate function that always returns true.
• alwaysFalse - predicate function that always returns false.

The predicate functions above are very useful as default function argument values, given that Dart does not allow declaring a lambda for a default argument value.

The catching functions return a Result<T> and never throw, which enforces that callers handle errors.

Extension functions

on <T> (any type, including nullable types)

• vmap - map over any value.
• apply - call a given function taking the receiver, return the receiver (asynchronous).
• apply$ - call a given function taking the receiver, return the receiver (asynchronous).

This is particularly convenient to capture fields, e.g. in cases like this:

class Person {
  final String? name;
  const Person(this.name);

  // DOES NOT COMPILE!
  // @override toString() {
    // if (name == null) return '<No name>';
    // Even though 'name' is final, a subtype could turn it into a mutable getter.
    // return name.capitalize();
  // }
  
  @override toString() {
    // using `vmap` and `apply`ing a side-effecting function 
    return name?.vmap((n) => n.capitilize()).apply(print) ?? '<No name>';
  }
}

on <T?> (any nullable type)

• vmapOr - map over the value if non-null, or provide a default value.
• orThrow - get the value if non-null, or throw an error otherwise.

orThrow exists due to Dart not allowing this:

Object? nullableValue = null;

// In Dart, this is ok:
final someValue = nullableValue ?? 'yes!';

// MISSING DART FUNCTIONALITY - DOES NOT COMPILE
final value = nullableValue ?? throw Exception('a good error message here');

// the '!' operator also does it, but does not give a good error for end users.
final nonNullValue = nullableValue!;

// orThrow to the rescue
final aValue = nullableValue.orThrow(() => ArgumentError('missing something', 'value'));

on int

• times - run some action N times, asynchronously.
• times$ - run some action N times, synchronously.
• timesIndex - run some action N times taking an iteration index, asynchronously.
• timesIndex$ - run some action N times taking an iteration index, synchronously.

The async times functions accept an optional waitIterations parameter which determines whether each iteration should wait for the previous one to complete before starting. By default, waitIterations is true. Setting it to false causes all iterations to start immediately.

on bool Function(T) and Future<bool> Function(T) (predicates)

• not - negate an asynchronous predicate.
• not$ - negate a synchronous predicate.

Examples

import 'package:conveniently/conveniently.dart';

/// Conveniently examples.
///
/// Functions whose name ends with '$' indicate they are "synchronous",
/// and dropping the '$' gives the corresponding async function's name.
void main() {
  // do something N times
  3.times$(() => print('Conveniently'));

  // with an index
  2.timesIndex$((i) => print('Conveniently $i'));

  // map over any value
  print(10.vmap((i) => i + 1)); // prints 11

  // nullable helpers make it more like Optional
  Object? nullable;
  nullable = 'foo';
  print(nullable.vmapOr((v) => 'v = $v', () => 'none')); // prints 'v = foo'
  print(nullable.orThrow(ArgumentError.new)); // prints 'foo'
  nullable = null;
  print(nullable.vmapOr((v) => 'v = $v', () => 'none')); // prints 'none'

  // vmap and vmapOr help writing pipelines with nullable values
  nullable
      .vmapOr((s) => 'Some $s', () => 'default value')
      .vmap((v) => 'v not null here: ${v.hashCode}')
      .apply$(print) // use side-effect operations with apply/apply$
      .vmap(
          (s) => print(s.toUpperCase())); // prints 'V NOT NULL HERE: 305987627'

  // `not` can be used to negate a predicate
  bool isEven(int n) => n % 2 == 0;
  final isOdd = isEven.not$;
  print([1, 2, 3, 4].where(isOdd)); // prints (1, 3)

  // convert Exceptions to values to enforce error checking
  final result = catching$(() => 'function that may throw');

  // pattern match to get a value out of Result
  print(switch (result) {
    Ok(value: var v) => 'Success: $v',
    Fail(exception: var e) => 'FAILURE: $e',
  });

  // or use the getters
  print('Result is error? ${result.isError}, '
      'success: ${result.successOrNull}, '
      'failure: ${result.failureOrNull}');
}

Other interesting helper libraries

• dart-quiver - Quiver is a set of utility libraries for Dart that makes using many Dart libraries easier and more convenient, or adds additional functionality.
• fpdart - All the main functional programming types and patterns fully documented, tested, and with examples.
• collection - Contains utility functions and classes in the style of dart:collection to make working with collections easier.

Quiver has lots of helper utilities grouped in a few libraries:

• quiver.async
• quiver.cache
• quiver.check
• quiver.collection
• quiver.core
• quiver.string
• quiver.time

And more...

But no tiny functions like conveniently.

fpdart is a much more comprehensive library for Functional Programming enthusiasts. conveniently doesn't try to provide anything like what fpdart does, (despite providing a few functions that are also helpful when doing FP) so it's a much smaller package.

collection provides lots of helper functions that work with Dart collections. It's pretty good at that, which is why conveniently does not attempt to provide collections helpers at all.