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Introduce IterableMapEntryExtension for use with Map.entries. #715

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merged 2 commits into from
Nov 5, 2024
Merged

Introduce IterableMapEntryExtension for use with Map.entries. #715

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672e51a
Introduce `IterableMapEntryExtension` for use with `Map.entries`.
jonasfj Nov 1, 2024
b9dc19c
Fix review comments
jonasfj Nov 5, 2024
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4 changes: 4 additions & 0 deletions pkgs/collection/CHANGELOG.md
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Original file line number Diff line number Diff line change
@@ -1,3 +1,7 @@
## 1.19.1-wip
- Add `IterableMapEntryExtension` for working on `Map` as a list of pairs, using
`Map.entries`.

## 1.19.1

- Move to `dart-lang/core` monorepo.
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37 changes: 37 additions & 0 deletions pkgs/collection/lib/src/iterable_extensions.dart
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Expand Up @@ -914,6 +914,43 @@ extension IterableIterableExtension<T> on Iterable<Iterable<T>> {
};
}

/// Extension on iterables of [MapEntry].
///
/// An [Iterable<MapEntry>] is obtained using [Map.entries]. These extensions
/// facilitates working directly on the entries of a [Map].
extension IterableMapEntryExtension<K, V> on Iterable<MapEntry<K, V>> {
/// The elements whose [MapEntry.key] values satisfy [test].
///
/// The resulting iterable is lazily computing its elements
/// based on the elements this iterable.
Iterable<MapEntry<K, V>> whereKey(bool Function(K) test) =>
where((e) => test(e.key));

/// The elements whose [MapEntry.value] values satisfy [test].
///
/// The resulting iterable is lazily computing its elements
/// based on the elements this iterable.
Iterable<MapEntry<K, V>> whereValue(bool Function(V) test) =>
where((e) => test(e.value));
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(Too bad where is taken, so it can't be where({bool Function(K)? key, bool Function(V)? value}))

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@jonasfj jonasfj Nov 5, 2024 •
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Yes, I feel the same with .map.

But I wouldn't make where({bool Function(K)? key, bool Function(V)? value}).
I would make: where(bool Function(K, V) test), ignoring a parameter in a closure is not that bad.

Maybe, we should consider adding:

  • wherePair(bool Function(K, V) test)
  • mapPair<T>(T Function(K, V) toElement)

We could consider adding such extension methods to:

  • Iterable<MapEntry<K, V>>, and,
  • Iterable<(A, B)>.

But that seems outside the scope of this PR.

And it's entirely possible that a language feature providing pattern matching in the signature of a closure is better.

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@lrhn lrhn Nov 6, 2024 •
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Maybe whereEntry/mapEntry/anyEntry/everyEntry with an X Function(K, V) argument. (Don't say "pair", it's not — just — a pair! It's a key-and-value.)
Some of those (not whereEntry) could be extensions to Map<K,V> too. (Not saying they should, but they could.)


/// A new lazy [Iterable] of the [MapEntry.key]s of these entries.
///
/// Do not use this getter as `map.entries.keys`, just use `map.keys`
/// directly.
Iterable<K> get keys => map((e) => e.key);

/// A new lazy [Iterable] of the [MapEntry.value]s of these entries.
///
/// Do not use this getter as `map.entries.values`, just use `map.values`
/// directly.
Iterable<V> get values => map((e) => e.value);

/// Create a [Map<K, V>] from all elements.
///
/// This is a short-hand for [Map.fromEntries].
Map<K, V> toMap() => Map<K, V>.fromEntries(this);
}

/// Extensions that apply to iterables of [Comparable] elements.
///
/// These operations can assume that the elements have a natural ordering,
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2 changes: 1 addition & 1 deletion pkgs/collection/pubspec.yaml
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@@ -1,5 +1,5 @@
name: collection
version: 1.19.1
version: 1.19.1-wip
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Should be 1.20.0, unless 1.19.0 hasn't been released yet.
(Adds new feature ⇒ minor version increment.)

description: >-
Collections and utilities functions and classes related to collections.
repository: https://github.com/dart-lang/core/tree/main/pkgs/collection
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174 changes: 174 additions & 0 deletions pkgs/collection/test/extensions_test.dart
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Expand Up @@ -1122,6 +1122,180 @@ void main() {
});
});
});
group('of MapEntry', () {
group('.whereKey', () {
test('empty', () {
expect(
iterable(<MapEntry<String, int>>[]).whereKey(unreachable),
isEmpty,
);
});
test('single', () {
expect(
iterable([const MapEntry('a', 1)]).whereKey((k) => k == 'a'),
[const MapEntry('a', 1)],
);
expect(
iterable([const MapEntry('a', 1)]).whereKey((k) => k == 'b'),
isEmpty,
);
});
test('multiple', () {
expect(
iterable([
const MapEntry('a', 1),
const MapEntry('b', 2),
]).whereKey((k) => k == 'a'),
[const MapEntry('a', 1)],
);
expect(
iterable([
const MapEntry('a', 1),
const MapEntry('b', 2),
]).whereKey((k) => k == 'b'),
[const MapEntry('b', 2)],
);
expect(
iterable([
const MapEntry('a', 1),
const MapEntry('b', 2),
]).whereKey((k) => k != 'c'),
[const MapEntry('a', 1), const MapEntry('b', 2)],
);
expect(
iterable([
const MapEntry('a', 1),
const MapEntry('b', 2),
const MapEntry('a', 3),
]).whereKey((k) => k == 'a'),
[const MapEntry('a', 1), const MapEntry('a', 3)],
);
});
});
group('.whereValue', () {
test('empty', () {
expect(
iterable(<MapEntry<String, int>>[]).whereValue(unreachable),
isEmpty,
);
});
test('single', () {
expect(
iterable([const MapEntry('a', 1)]).whereValue((v) => v == 1),
[const MapEntry('a', 1)],
);
expect(
iterable([const MapEntry('a', 1)]).whereValue((v) => v == 2),
isEmpty,
);
});
test('multiple', () {
expect(
iterable([
const MapEntry('a', 1),
const MapEntry('b', 2),
]).whereValue((v) => v == 1),
[const MapEntry('a', 1)],
);
expect(
iterable([
const MapEntry('a', 1),
const MapEntry('b', 2),
]).whereValue((v) => v == 2),
[const MapEntry('b', 2)],
);
expect(
iterable([
const MapEntry('a', 1),
const MapEntry('b', 2),
]).whereValue((v) => v != 3),
[const MapEntry('a', 1), const MapEntry('b', 2)],
);
expect(
iterable([
const MapEntry('a', 1),
const MapEntry('b', 2),
const MapEntry('c', 1),
]).whereValue((v) => v == 1),
[const MapEntry('a', 1), const MapEntry('c', 1)],
);
expect(
iterable([
const MapEntry('a', 1),
const MapEntry('b', 2),
const MapEntry('a', 1),
]).whereValue((v) => v == 1),
[const MapEntry('a', 1), const MapEntry('a', 1)],
);
});
});
group('.keys', () {
test('empty', () {
expect(iterable(<MapEntry<String, int>>[]).keys, isEmpty);
});
test('single', () {
expect(iterable([const MapEntry('a', 1)]).keys, ['a']);
});
test('multiple', () {
expect(
iterable([const MapEntry('a', 1), const MapEntry('b', 2)]).keys,
['a', 'b'],
);
expect(
iterable([
const MapEntry('a', 1),
const MapEntry('b', 2),
const MapEntry('a', 3),
]).keys,
['a', 'b', 'a'],
);
});
});
group('.values', () {
test('empty', () {
expect(iterable(<MapEntry<String, int>>[]).values, isEmpty);
});
test('single', () {
expect(iterable([const MapEntry('a', 1)]).values, [1]);
});
test('multiple', () {
expect(
iterable([const MapEntry('a', 1), const MapEntry('b', 2)]).values,
[1, 2],
);
expect(
iterable([
const MapEntry('a', 1),
const MapEntry('b', 2),
const MapEntry('a', 3),
]).values,
[1, 2, 3],
);
});
});
group('.toMap', () {
test('empty', () {
expect(iterable(<MapEntry<String, int>>[]).toMap(), <String, int>{});
});
test('single', () {
expect(iterable([const MapEntry('a', 1)]).toMap(), {'a': 1});
});
test('multiple', () {
expect(
iterable([const MapEntry('a', 1), const MapEntry('b', 2)]).toMap(),
{'a': 1, 'b': 2},
);
expect(
iterable([
const MapEntry('a', 1),
const MapEntry('b', 2),
const MapEntry('a', 3),
]).toMap(),
{'b': 2, 'a': 3},
);
});
});
});
group('of comparable', () {
group('.min', () {
test('empty', () {
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