CollectionsMarshal.GetValueRef(Dictionary)

[benaadams]

Implement the api

namespace System.Runtime.InteropServices
{
    public static class CollectionsMarshal
    {
        public ref TValue GetValueRefOrNullRef<TKey, TValue>(Dictionary<TKey, TValue> dictionary, TKey key);
    }
}

Contributes to #27062

/cc @layomia

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Issue Details

---

Still needs doc comments and tests

Resolves #27062

Author:	benaadams
Assignees:	-
Labels:	area-System.Collections
Milestone:	-

[stephentoub]

Still needs doc comments and tests

Are there places outside of Dictionary we should be using the new method, too?

[benaadams]

Are there places outside of Dictionary we should be using the new method, too?

For GetValueRef the big wins are for struct TValues; either using in place or mutating which don't look to be a common pattern in CoreLib.

However GetValueRefOrAddDefault does look like it would have more applicability removing a double lookup from TryGet+Add; assuming it was implemented more efficiently. So is probably worth looping back and doing that as well.

[jkotas]

GetValueRefOrAddDefault does look like it would have more applicability removing a double lookup from TryGet+Add

It also needs to be something reasonably hot to make it worth the trouble.

[benaadams]

It also needs to be something reasonably hot to make it worth the trouble.

While CoreLib does create dictionaries, it doesn't really do much modifying of them and alas my search-fu isn't good enough to check all the other libs; though I definitely have uses further downstream

Looks like a ref enumerator

ref struct RefEnumerator
{
    (TKey key, ref TValue) Current { get; }
    bool MoveNext();
}

would be helpful too, but small steps 😉

[stephentoub]

Thanks, @benaadams.

[benaadams]

runtime (Libraries Test Run checked coreclr windows x64 Debug) Failure is #48236 though that's closed, and looks like the vm pool died for the rest

[benaadams]

Rebased to reset CI

[benaadams]

🥳