What's wrong
ContiguousMap<TKey,TValue>'s indexer setter (Containers/ContiguousMap.cs:178) handles an existing key with:
if (keyToIndex.TryGetValue(key, out int index))
{
// Key exists, update the value
items[index] = new Entry(key, value);
}It writes the caller's key into the entry, not the key that was stored first. With a custom comparer, the key in items stops matching the key held in keyToIndex.
Repro
var m = new ContiguousMap<string, int>(StringComparer.OrdinalIgnoreCase);
m["Apple"] = 1;
m["APPLE"] = 2;
// Keys / foreach / AsSpan() now report "APPLE"
// keyToIndex still holds "Apple"
- Actual:
Keys, enumeration and AsSpan() return "APPLE".
- Expected:
"Apple", with value 2. Dictionary<,> behaves this way, and so do the sibling InsertionOrderMap and OrderedMap, which update only the value.
I confirmed this in a scratch console app against the current main.
Why it matters
Updating a value silently changes a key's identity, and only in this one map type. Two cases are affected:
- Code that swaps
InsertionOrderMap/Dictionary for ContiguousMap for performance gets different keys back.
- Any case-insensitive or otherwise normalising comparer gets its keys rewritten by whichever caller spelling came last.
Suggested fix
items[index] = new Entry(items[index].Key, value);
Add a regression test that uses a case-insensitive comparer and asserts the original key's casing survives an update through the indexer.
What's wrong
ContiguousMap<TKey,TValue>'s indexer setter (Containers/ContiguousMap.cs:178) handles an existing key with:It writes the caller's key into the entry, not the key that was stored first. With a custom comparer, the key in
itemsstops matching the key held inkeyToIndex.Repro
Keys, enumeration andAsSpan()return"APPLE"."Apple", with value 2.Dictionary<,>behaves this way, and so do the siblingInsertionOrderMapandOrderedMap, which update only the value.I confirmed this in a scratch console app against the current
main.Why it matters
Updating a value silently changes a key's identity, and only in this one map type. Two cases are affected:
InsertionOrderMap/DictionaryforContiguousMapfor performance gets different keys back.Suggested fix
Add a regression test that uses a case-insensitive comparer and asserts the original key's casing survives an update through the indexer.