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const None can break methods due to Never (#92)
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@SandroMaglione
SandroMaglione authored Mar 2, 2023
2 parents 9582ee3 + 9b3e786 commit ba35396
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Showing 8 changed files with 88 additions and 305 deletions.
6 changes: 3 additions & 3 deletions example/json_serializable/test/user_test.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -41,9 +41,9 @@ void main() {
"phone": null,
});

expect(user.id, isA<None<dynamic>>());
expect(user.birthDate, isA<None<dynamic>>());
expect(user.phone, isA<None<dynamic>>());
expect(user.id, isA<None>());
expect(user.birthDate, isA<None>());
expect(user.phone, isA<None>());
});

test('fromJson (Some)', () {
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4 changes: 2 additions & 2 deletions example/src/option/overview.dart
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Original file line number Diff line number Diff line change
@@ -1,7 +1,7 @@
import 'package:fpdart/fpdart.dart';

/// Don't do that! ⚠
int divideI(int x, int y) => x ~/ y; /// this will throw if y == 0
int divideI(int x, int y) => x ~/ y; // this will throw if y == 0

/// Error handling without exceptions using [Option] 🎉
Option<int> divideF(int x, int y) {
Expand All @@ -17,7 +17,7 @@ Option<int> divide2F(int x, int y) => Option.tryCatch(() => x ~/ y);
void main() {
// --- Initialize an Option 👇 --- //
const someInit = Some(10);
const noneInit = None<int>();
const noneInit = None();

final someInit2 = some(10);
final noneInit2 = none<int>();
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210 changes: 53 additions & 157 deletions lib/src/option.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -2,12 +2,10 @@ import 'either.dart';
import 'function.dart';
import 'task_option.dart';
import 'tuple.dart';
import 'typeclass/alt.dart';
import 'typeclass/applicative.dart';
import 'typeclass/eq.dart';
import 'typeclass/extend.dart';
import 'typeclass/filterable.dart';
import 'typeclass/foldable.dart';
import 'typeclass/functor.dart';
import 'typeclass/hkt.dart';
import 'typeclass/monad.dart';
Expand All @@ -23,7 +21,7 @@ Option<T> some<T>(T t) => Some(t);
/// Return a [None].
///
/// Shortcut for `Option.none()`.
Option<T> none<T>() => None<T>();
Option<T> none<T>() => const Option.none();

/// Return [None] if `t` is `null`, [Some] otherwise.
///
Expand Down Expand Up @@ -68,76 +66,10 @@ abstract class Option<T> extends HKT<_OptionHKT, T>
Functor<_OptionHKT, T>,
Applicative<_OptionHKT, T>,
Monad<_OptionHKT, T>,
Foldable<_OptionHKT, T>,
Alt<_OptionHKT, T>,
Extend<_OptionHKT, T>,
Filterable<_OptionHKT, T> {
const Option();

/// Return the result of `f` called with `b` and the value of [Some].
/// If this [Option] is [None], return `b`.
@override
B foldRight<B>(B b, B Function(B acc, T t) f);

/// Return the result of `f` called with `b` and the value of [Some].
/// If this [Option] is [None], return `b`.
@override
B foldLeft<B>(B b, B Function(B acc, T t) f) =>
foldMap<Endo<B>>(dualEndoMonoid(), (a) => (B b) => f(b, a))(b);

/// Use `monoid` to combine the value of [Some] applied to `f`.
@override
B foldMap<B>(Monoid<B> monoid, B Function(T t) f) =>
foldRight(monoid.empty, (b, a) => monoid.combine(f(a), b));

/// Return the result of `f` called with `b` and the value of [Some].
/// If this [Option] is [None], return `b`.
@override
B foldRightWithIndex<B>(B b, B Function(int i, B acc, T t) f) =>
foldRight<Tuple2<B, int>>(
Tuple2(b, length() - 1),
(t, a) => Tuple2(f(t.second, t.first, a), t.second - 1),
).first;

/// Return the result of `f` called with `b` and the value of [Some].
/// If this [Option] is [None], return `b`.
@override
B foldLeftWithIndex<B>(B b, B Function(int i, B acc, T t) f) =>
foldLeft<Tuple2<B, int>>(
Tuple2(b, 0),
(t, a) => Tuple2(f(t.second, t.first, a), t.second + 1),
).first;

/// Returns `1` when [Option] is [Some], `0` otherwise.
@override
int length() => foldLeft(0, (b, _) => b + 1);

/// Return the result of `predicate` applied to the value of [Some].
/// If the [Option] is [None], returns `false`.
@override
bool any(bool Function(T t) predicate) => foldMap(boolOrMonoid(), predicate);

/// Return the result of `predicate` applied to the value of [Some].
/// If the [Option] is [None], returns `true`.
@override
bool all(bool Function(T t) predicate) => foldMap(boolAndMonoid(), predicate);

/// Use `monoid` to combine the value of [Some].
@override
T concatenate(Monoid<T> monoid) => foldMap(monoid, identity);

/// Return the value of this [Option] if it is [Some], otherwise return `a`.
@override
Option<T> plus(covariant Option<T> a);

/// Return `Some(a)`.
@override
Option<T> prepend(T t) => Some(t);

/// If this [Option] is [None], return `Some(a)`. Otherwise return this [Some].
@override
Option<T> append(T t);

/// Change the value of type `T` to a value of type `B` using function `f`.
/// ```dart
/// /// Change type `String` (`T`) to type `int` (`B`)
Expand Down Expand Up @@ -251,16 +183,6 @@ abstract class Option<T> extends HKT<_OptionHKT, T>
Option<B> flatMapThrowable<B>(B Function(T t) f) =>
flatMap((t) => Option.tryCatch(() => f(t)));

/// Return the current [Option] if it is a [Some], otherwise return the result of `orElse`.
///
/// Used to provide an **alt**ernative [Option] in case the current one is [None].
/// ```dart
/// [🍌].alt(() => [🍎]) -> [🍌]
/// [_].alt(() => [🍎]) -> [🍎]
/// ```
@override
Option<T> alt(covariant Option<T> Function() orElse);

/// Change the value of [Option] from type `T` to type `Z` based on the
/// value of `Option<T>` using function `f`.
@override
Expand All @@ -273,7 +195,8 @@ abstract class Option<T> extends HKT<_OptionHKT, T>
/// If this [Option] is a [Some] and calling `f` returns `true`, then return this [Some].
/// Otherwise return [None].
@override
Option<T> filter(bool Function(T t) f);
Option<T> filter(bool Function(T t) f) =>
flatMap((t) => f(t) ? this : const Option.none());

/// If this [Option] is a [Some] and calling `f` returns [Some], then return this [Some].
/// Otherwise return [None].
Expand Down Expand Up @@ -350,36 +273,24 @@ abstract class Option<T> extends HKT<_OptionHKT, T>
/// Return `true` when value is [None].
bool isNone();

/// If this [Option] is a [Some] then return the value inside the [Option].
/// Otherwise return the result of `orElse`.
/// ```dart
/// [🍌].getOrElse(() => 🍎) -> 🍌
/// [_].getOrElse(() => 🍎) -> 🍎
///
/// 👆 same as 👇
///
/// [🍌].match(() => 🍎, (🍌) => 🍌)
/// ```
T getOrElse(T Function() orElse);

/// Return value of type `T` when this [Option] is a [Some], `null` otherwise.
T? toNullable();

/// Build an [Either] from [Option].
///
/// Return [Right] when [Option] is [Some], otherwise [Left] containing
/// the result of calling `onLeft`.
Either<L, T> toEither<L>(L Function() onLeft);
Either<L, T> toEither<L>(L Function() onLeft) => match(
() => Left(onLeft()),
Right.new,
);

/// Convert this [Option] to a [TaskOption].
///
/// Used to convert a sync context ([Option]) to an async context ([TaskOption]).
/// You should convert [Option] to [TaskOption] every time you need to
/// call an async ([Future]) function based on the value in [Option].
TaskOption<T> toTaskOption();

/// Return `true` when value of `a` is equal to the value inside the [Option].
bool elem(T t, Eq<T> eq);
TaskOption<T> toTaskOption() => TaskOption(() => Future.value(this));

/// {@template fpdart_traverse_list_option}
/// Map each element in the list to an [Option] using the function `f`,
Expand Down Expand Up @@ -471,7 +382,7 @@ abstract class Option<T> extends HKT<_OptionHKT, T>
predicate(value) ? Some(f(value)) : Option.none();

/// Return a [None].
const factory Option.none() = None<T>;
const factory Option.none() = None;

/// Return a `Some(a)`.
const factory Option.of(T t) = Some<T>;
Expand Down Expand Up @@ -584,18 +495,9 @@ class Some<T> extends Option<T> {
@override
Option<B> map<B>(B Function(T t) f) => Some(f(_value));

@override
B foldRight<B>(B b, B Function(B acc, T t) f) => f(b, _value);

@override
Option<B> flatMap<B>(covariant Option<B> Function(T t) f) => f(_value);

@override
T getOrElse(T Function() orElse) => _value;

@override
Option<T> alt(Option<T> Function() orElse) => this;

@override
B match<B>(B Function() onNone, B Function(T t) onSome) => onSome(_value);

Expand All @@ -618,20 +520,11 @@ class Some<T> extends Option<T> {
);

@override
T? toNullable() => _value;

@override
bool elem(T t, Eq<T> eq) => eq.eqv(_value, t);
T toNullable() => _value;

@override
Either<L, T> toEither<L>(L Function() onLeft) => Right(_value);

@override
Option<T> plus(covariant Option<T> a) => this;

@override
Option<T> append(T t) => this;

@override
bool operator ==(Object other) => (other is Some) && other._value == _value;

Expand All @@ -648,38 +541,32 @@ class Some<T> extends Option<T> {
TaskOption<T> toTaskOption() => TaskOption.of(_value);
}

class None<T> extends Option<T> {
class None extends Option<Never> {
const None();

@override
Option<D> map2<C, D>(covariant Option<C> mc, D Function(T t, C c) f) =>
flatMap((b) => mc.map((c) => f(b, c)));

@override
Option<E> map3<C, D, E>(covariant Option<C> mc, covariant Option<D> md,
E Function(T t, C c, D d) f) =>
flatMap((a) => mc.flatMap((c) => md.map((d) => f(a, c, d))));

@override
Option<B> map<B>(B Function(T t) f) => const Option.none();

@override
B foldRight<B>(B b, B Function(B acc, T t) f) => b;
Option<D> map2<C, D>(covariant Option<C> mc, D Function(Never t, C c) f) =>
this;

@override
Option<B> flatMap<B>(covariant Option<B> Function(T t) f) => Option<B>.none();
Option<E> map3<C, D, E>(
covariant Option<C> mc,
covariant Option<D> md,
E Function(Never t, C c, D d) f,
) =>
this;

@override
T getOrElse(T Function() orElse) => orElse();
Option<B> map<B>(B Function(Never t) f) => this;

@override
Option<T> alt(Option<T> Function() orElse) => orElse();
Option<B> flatMap<B>(covariant Option<B> Function(Never t) f) => this;

@override
B match<B>(B Function() onNone, B Function(T t) onSome) => onNone();
B match<B>(B Function() onNone, B Function(Never t) onSome) => onNone();

@override
Option<Z> extend<Z>(Z Function(Option<T> t) f) => const Option.none();
Option<Z> extend<Z>(Z Function(Option<Never> t) f) => const Option.none();

@override
bool isSome() => false;
Expand All @@ -688,28 +575,13 @@ class None<T> extends Option<T> {
bool isNone() => true;

@override
Option<T> filter(bool Function(T t) f) => const Option.none();

@override
Option<Z> filterMap<Z>(Option<Z> Function(T t) f) => const Option.none();

@override
T? toNullable() => null;

@override
bool elem(T t, Eq<T> eq) => false;

@override
Either<L, T> toEither<L>(L Function() onLeft) => Left(onLeft());
Option<Z> filterMap<Z>(Option<Z> Function(Never t) f) => const Option.none();

@override
Option<T> plus(covariant Option<T> a) => a;

@override
Option<T> append(T t) => Some(t);
bool operator ==(Object other) => other is None;

@override
bool operator ==(Object other) => other is None;
Null toNullable() => null;

@override
int get hashCode => 0;
Expand All @@ -718,8 +590,32 @@ class None<T> extends Option<T> {
String toString() => 'None';

@override
Object? toJson(Object? Function(T p1) toJsonT) => null;
Object? toJson(Object? Function(Never p1) toJsonT) => null;
}

@override
TaskOption<T> toTaskOption() => TaskOption.none();
extension OptionExtension<T> on Option<T> {
/// Return the current [Option] if it is a [Some], otherwise return the result of `orElse`.
///
/// Used to provide an **alt**ernative [Option] in case the current one is [None].
/// ```dart
/// [🍌].alt(() => [🍎]) -> [🍌]
/// [_].alt(() => [🍎]) -> [🍎]
/// ```
Option<T> alt(Option<T> Function() orElse) =>
this is Some<T> ? this : orElse();

/// Return `true` when value of `a` is equal to the value inside the [Option].
bool elem(T t, Eq<T> eq) => match(() => false, (value) => eq.eqv(value, t));

/// If this [Option] is a [Some] then return the value inside the [Option].
/// Otherwise return the result of `orElse`.
/// ```dart
/// [🍌].getOrElse(() => 🍎) -> 🍌
/// [_].getOrElse(() => 🍎) -> 🍎
///
/// 👆 same as 👇
///
/// [🍌].match(() => 🍎, (🍌) => 🍌)
/// ```
T getOrElse(T Function() orElse) => match(orElse, identity);
}
6 changes: 3 additions & 3 deletions test/src/either_test.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -443,7 +443,7 @@ void main() {
test('Left', () {
final value = Either<String, int>.left('none');
final ap = value.toOption();
expect(ap, isA<None<int>>());
expect(ap, isA<None>());
});
});

Expand Down Expand Up @@ -525,7 +525,7 @@ void main() {
test('Right', () {
final value = Either<String, int>.of(10);
final ap = value.getLeft();
expect(ap, isA<None<String>>());
expect(ap, isA<None>());
});

test('Left', () {
Expand All @@ -549,7 +549,7 @@ void main() {
test('Left', () {
final value = Either<String, int>.left('none');
final ap = value.getRight();
expect(ap, isA<None<int>>());
expect(ap, isA<None>());
});
});

Expand Down
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