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Use values iterator and update in map equality/hash #718

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merged 4 commits into from
Nov 6, 2024
Merged

Use values iterator and update in map equality/hash #718

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80007b5
use .entries and .update in map equality
jakemac53 Nov 4, 2024
6b19fb0
add changelog entry
jakemac53 Nov 5, 2024
314c1e1
use values iterator
jakemac53 Nov 5, 2024
04e12bb
add static helpers and use tearoffs
jakemac53 Nov 6, 2024
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3 changes: 3 additions & 0 deletions pkgs/collection/CHANGELOG.md
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Original file line number Diff line number Diff line change
@@ -1,6 +1,9 @@
## 1.19.1-wip

- Add `IterableMapEntryExtension` for working on `Map` as a list of pairs, using
`Map.entries`.
- Optimize equality and hash code for maps by using `update` and a `values`
iterator to avoid extra lookups.

## 1.19.1

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21 changes: 13 additions & 8 deletions pkgs/collection/lib/src/equality.dart
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Expand Up @@ -325,16 +325,19 @@ class MapEquality<K, V> implements Equality<Map<K, V>> {
var length = map1.length;
if (length != map2.length) return false;
Map<_MapEntry, int> equalElementCounts = HashMap();
var values1 = map1.values.iterator;
for (var key in map1.keys) {
var entry = _MapEntry(this, key, map1[key]);
var count = equalElementCounts[entry] ?? 0;
equalElementCounts[entry] = count + 1;
var value = (values1..moveNext()).current;
var entry = _MapEntry(this, key, value);
equalElementCounts.update(entry, (i) => i + 1, ifAbsent: () => 1);
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}
final values2 = map2.values.iterator;
for (var key in map2.keys) {
var entry = _MapEntry(this, key, map2[key]);
var count = equalElementCounts[entry];
if (count == null || count == 0) return false;
equalElementCounts[entry] = count - 1;
var value = (values2..moveNext()).current;
var entry = _MapEntry(this, key, value);
var count =
equalElementCounts.update(entry, (i) => i - 1, ifAbsent: () => -1);
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if (count < 0) return false;
}
return true;
}
Expand All @@ -343,9 +346,11 @@ class MapEquality<K, V> implements Equality<Map<K, V>> {
int hash(Map<K, V>? map) {
if (map == null) return null.hashCode;
var hash = 0;
var values = map.values.iterator;
for (var key in map.keys) {
var value = (values..moveNext()).current;
var keyHash = _keyEquality.hash(key);
var valueHash = _valueEquality.hash(map[key] as V);
var valueHash = _valueEquality.hash(value);
hash = (hash + 3 * keyHash + 7 * valueHash) & _hashMask;
}
hash = (hash + (hash << 3)) & _hashMask;
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